Hindusim can be related to atheism, by simply not believing in god. Sub-conciously, all buddhists, jains are hindu's.
I have read that argument, and it is certainly easier to see the Devas and their avatars as allegories in Hinduism than to make a similar effort in the Abrahamic religions.
I can see that there is a point to it, too. The Sanatana Dharma has plenty of worth without necessarily relying on belief in God. It does inspire and reminds one of the worth of Transcendence.
Still, it is a bit tricky at times, or so it seems to me. There
is a lot of emphasys on the Devas and Avatars, and most of the time they seem to be actively acting.
I don't really agree that Buddhism should be considered part of Hinduism, although it is hardly a matter worth becoming sour about. I do recognize that most early Buddhist concepts are directly inherited from Hinduism (though that is hardly the case anymore except in Tibetan and Nepalese Vajrayana) and that, since both are religions, by necessity they end up having somewhat convergent goals, if not necessarily the same ideas about how to reach them.
Then again, I usually think of Hinduism as a framework of sorts, an "assembly kit" of sorts, as opposed to a ready-made religion. It offers tools, but does not really even attempt to have the same universal face among its various subgroups. It does, however, offer a common language and various useful concepts. It is up to more specific Gurus and practicioners to build a coherent faith (and discuss it) from there.
As for the OP and Poll - what would "Gnostici" be? Never heard of it. I am quite atheistic, so I suppose that if I were to leave Buddhism I would probably choose Taoism, perhaps even Hinduism. It depends a fair lot from which communities (
Sanghas) I had access to.