Biblicalia posts a fascinating account of the alleged deathbed conversion of the Nasi Hillel ii.
One interesting point is the fact that a Christian Bishop should be called in for medical reasons. We find a parallel to this in the Talmud - Avodah Zarah 28a:
"What about R. Abbahu, who too was a distinguished man, yet Jacob the Min prepared for him a medicine for his leg, and were it not for R. Ammi and R. Asi who licked his leg, he would have cut his leg off? - The one [who attended] R. Johanan was an expert physician. - So too was that of R. Abbahu, an expert physician! - It was different in the case of R. Abbahu, for Minim adopt the attitude of let me die with the Philistines."
Jacob the Min (who is mentioned fairly frequently in the Talmud) has been identified by some I forget where I saw this) with the apostle James (I don't know which one). Now R' Abbahu live only several decades before Hillel II so it isn't so far fetched to say that Hillel would call a Bishop for medical reasons.
On the other hand, if this were true, one would expect a reference to this in Rabbinic literature. Specifically, Kiddushin 40b:
ר"ש בן יוחי אומר אפילו צדיק גמור כל ימיו ומרד באחרונה איבד את הראשונות שנאמר (יחזקאל לג) צדקת הצדיק לא תצילנו ביום פשעו ואפילו רשע גמור כל ימיו ועשה תשובה באחרונה אין מזכירים לו שוב רשעו שנאמר (יחזקאל לג) ורשעת הרשע לא יכשל בה ביום שובו מרשעו וניהוי כמחצה עונות ומחצה זכיות אמר ריש לקיש בתוהא על הראשונות
would have been the perfect place to mention Hillel II. Yet again, deathbed conversions, retractions and the like are all very convenient since they can't be easily refuted (as in here) Further, Epiphanius would definitely have it out for Hillel since he was close to Julian the apostate (see the letter quoted in the WP article) who was the arch-enemy of the Christians (For the same reason the account concerning Gamaliel V also needs to be taken with a large grain of salt.)
(See part 2 of R. Kimelman's dissertation on R' Yochanan of Tiberias for a full discussion of the relations between Jews and Christians during 3rd century Palestine - about a century before the time of Hillel II)
[Update:Biblicalia posts the full account of "Magic and A Patriarch".
I thank him for leaving the following important comment:
My own impression is that this Count Joseph, the Tiberian convert, was spinning some tales. As a convert, such a practice is not uncommon, of painting one's past associates in an unflattering light (in the case of Gamaliel V) and elevating certain beloved and respected former associates to one's own perceived post-conversion superiority (as in the case of Hillel II). I'd lay the onus on Joseph for these stories, as Epiphanius does indicate that he's the sole source for them. And as it's explicitly stated that Joseph was made a count by Constantine, Julian's hated uncle, there was likely some backlash that Joseph did experience, and which, as you suggested, tainted his memories of Gamaliel V, influencing him to tell the peculiar tale (which I'll also post for your benefit) of the rather lurid love-magic done for him, like something out of one of those old Greek romances.
The Jacob/James you mention wouldn't be any of the apostles, strictly so-called, as they all lived and died in the first century. It's such a common name, it would be hard to tell who R. Abbahu's physician may have been. We'd need more precision.
But I don't find it unlikely that people of a higher socioeconomic level would find calling on one another for matters such as health (and wealth) at all unusual. There may be quibbling about it later from inferiors, but there are some things that wealthy people simply did for one another that was more a part of intra-class courtesy than anything else. This tends to be forgotten.]
[Update 2:Menachem Mendel send us to Studia Patristica 32 - which in turn references an article in the JBL 60,4 The Textual History of an Aramaic Proverb (Traces of the Ebionean Gospel), Luitpold Wallach. The focus there is the famous account in Shabbos 116a concerning the dialogue between Imma Shalom ,the sister of Rabban Gamliel, Rabban Gamliel and an unnamed "philosopher". The following passage relates to our discussion (C refers to the TB version of the narrative):
It is not for nothing that Gamaliel has been connected with the Ebionites. We have the report of Epiphanius, Haeres., XXX, 4, who delivers it not without reserve after a certain Joseph, that the later Patriarch Hillel II, the descendent of Gamaliel's family, was converted to Christianity as a young man.18 Karl Holl was right in pointing out that this legend is due to the older legend that the earlier Gamaliel was a convert.19 The connection of Gamaliel II 20 with the Ebionean tradition in C thus turns out to serve but one purpose: to refute the fantastic claim laid by the Ebionites to an heir of the house of Gamaliel. This claim must have been known to the Jewish redactor of the "historized" version C, for it is only upon this assumption that the part of Gamaliel and of his sister in C becomes really understandable. The unmasking of the Ebionean Jewish-Christian on the part of Gamaliel implies the refutation of any claim]
Tal Ilan in The Quest for the Historical Beruriah, Rachel, and Imma Shalom, AJS Review 22,1 seems to be unaware of this source.
[I'm going to move this back eventually so as to keep all the Hoffman posts together)