Has he remarried his original wife that God recognizes? Yes.
Has he married into adultery? If he is still in the adulterous union, no.
If he has repented of the adultery, disengaged from it(i.e. divorce #2) and now walks in newness of life ... maybe :)
Don't forget the part about reaping what he has sown. :(
This is a new take on this that I'd never heard before.
Isn't there an old testament restriction on divorced people remarrying the same person if that person has in the interim gotten married and divorced again?