look man, you're just defining people living with (what you call) Hindu culture as followers of he Hindu religion - or that because there is a sect that argues that god can't be observed they're atheists.
it doesn't hold water. first you should define Hindus as something, that they believe in something - let's say that they believe in karma, and now after saying that they're incompatible with atheism. just saying that hindus just follow rituals and believe whatever they want doesn't work either because they follow different sets of rituals from each other. heck, everyone on the planet could be said to be a hindu on those basis.
doesn't really help that most hindus have polytheistic view and believe in spirits and all other kinds of superstitious things - that is magic and spirits. Richard Dawkins celebrates christmas and for sure saying that he is a christian would be wrong.
on the whole for most hindus to be a hindu is to believe in some magic or another, some deity or multiple deities or multiple appearances of the same deity in different forms. sure that goes with bona fide atheism just like a fish goes with a bicycle.