Hi, Steve!
Emmet, I think most scholars accept that Hebrews was written either by Paul or a traveling companion of his like Luke or Barnabas or Apollos. And it was'nt written that late, presumably in the 60s. So i don't see any reason to call it's doctrine questionable.
I think that most responsible scholars will acknowledge that there is no firm evidence for identifying the person who wrote Hebrews. The letter features argumentation and imagery that is uncommon to Pauline standards, and the IVP Dictionary article states that the letter's Greek style is "far superior in vocabulary and sentence construction to that of Paul." My own skills in Greek are insufficient to make such a judgment, but I expect the scholarship in the IVP series to trend toward the moderate or conservative end of things. The fleeting reference to Timothy in the close of the letter (13:23) does not demonstrate companionship with Paul, nor can it be taken for granted that this Timothy is the same individual known from the Pauline corpus.
Comments in the early church reveal a diversity of opinion about the author of the letter, and I would expect that if someone of blessed memory like Luke or Barnabas had authored it, the halo would have remained with the document, so to speak. Even lesser figures like Jude and Clement received documents attached to their memory, so for Hebrews to have survived with a cloud of doubt around its authorship, it suggests that the author was rather an unremarkable figure in the early church.
It seems, from internal evidence (2:3), that the author did not have direct experience of Jesus of Nazareth - which automatically suggests a greater margin of differentiation between his perspectives and the actual historical character of Jesus. Like Paul, the author's understanding of Jesus is formed in circumstances removed from the historical ministry of Jesus, and as such their Christologies have a greater likelihood of innovation and susceptibility to extraneous influence. Paul's Christology seems to have been processed in light of his personal mystical experience and his Hellenistic environment. The author of Hebrews appears to have processed his Christology through a creative engagement of the biblical text; this may have been the fruit of his own study, or inherited in whole or in part from others. But both processes are quite naturally open to deviation from the precedent and perspective of Jesus himself.
When I referred to the document's late acceptance, I was referring to its canonization process, not its date of composition (about which there apparently is no broad scholarly consensus). The canonical candidacy of Hebrews appears to have been debated for a long time, lasting into the fourth or perhaps even the fifth century.
Shalom,
Emmet
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