We expect it certainly, from the extended Gibbs Principle that states every vertebrate will exhibit an uneradicatible, endemic level of TSE disease from natural germline and somatic mutation. So far, chickens are only non-mammal for which the primary structure of prion is known.
Homology is always complicated by the potential fusion of remote individual domains.
So far a mammal probe has been used in chicken, but a degenerate chicken probe has not been used in mammals. Thus mammals could, in fact, have an undetected additional prion-like gene with a corresponding second form of prionic disease. One special problem with chicken prion is its hexapeptide repeat, which occurs in 9 rather faithful copies. This is evidently a very labile region. We can't rule out, without more sequences from the lower vertebrates, the worry that birds normally have a 4-5 fold repeat, and that the 9 repeats in domestic chicken correspond to comparable pathogenic inserts seen in humans.