What version is published online under "ahead of print" for an accepted paper?
Depends on journal policies. The one I'm most familiar with, the "ahead of print" articles are complete in every way except they've not been assigned to a volume &amp; issue. If this is the case for you then of course they will send proofs to the author before putting it there.

Alternatively they can put the accepted manuscript there. If this is the case it will look very unpolished; it might not be in the journal's style, the figures might be on separate pages, and so on. 

A glance at the articles already in the "ahead of print" section should reveal which is the case for you.