Personally in my campaign I would allow them to be compatible. Dervosh was made before Spell Combat so it did not mention it. In fact I would say that the only reason Spell Combay says it is a full round action is because it is not only an attack but a spell too.
I believe that the bonus slots could still be used for your lower level spells, at least that is how we have always played. I do not think that I have ever seen anything written against this either.
