1. Lorkhan is indeed a dead god, but seeing as he's a god, that's not saying much. In a less cryptic sense, Lorkhan just doesn't hold his original corporeal form, whatever that may be, though he DOES appear in avatars and myth-echos. Pelinal and the Underking(s) are examples of these.
2. Yeah. The Tribunal killed him, if not just Vehk. VIVEC didn't, but Vehk the mortal did.
3. I don't think Ayem and Seht ever expressed this, but I don't see why not. http://www.imperial-library.info/obscure_text/vehk_teaching.shtml, though I don't think he favors a SPECIFIC myth, though he does know that Lorkhan created it.
That is an odd question you asked though: not too many deny he created it.... The only ones I know that never EXPLICITLY stated he created it http://www.imperial-library.info/obscure_text/tsaesci.shtml, but them b*tches are scary. And homotheistic. And just bad as [censored].