>The form *wenh1-us- avoids the difficulty that Old Latin *venos should have
undergone /o/-umlaut of the /e/ in this >position, with a simple nasal
between the vowels and /w/, /h/, or zero before the /e/. >We should expect
Lat. *vonus, not <venus>, from an /es/-stem.
Sihler discusses PIE *e > Latin *o before *w or l pinguis, and after
consonant +w, then says, "Evidence for *we > Latin wo in other environments
is scanty and suspect. ... A better case can be made for PIE *wemh1 > vomo
... Elsewhere *we- > vo only before l pinguis ..."
So I'm not convinced we should expect *vonos from PIE *venos. As for
*venh1-os, the slight evidence there is (PIE *vemh1o) suggests the h1 would
not prevent this change (if there were such a change).
Peter