Problem is it’s so hard to define these terms. For example, were the ancient Egyptians ‘religious”? We tend to think so, judging by their statues, their Book of the Dead etc. Yet I was listening to an interview with an expert Egyptologist who said that our word “god” was not appropriate to what the Egyptians believed in.  So if we describe them as religious, theirs would have to be a religion without gods. Very odd.

Try reading the Corpus Hermeticum. The 'God' of this text is not the God of monotheism but that of the perennial philosophy, which can be said to reject both theism and atheism as extreme views.

The Corpus can be read as religion with no God, just as can Buddhism, Philosophical Taoism, Sufism, the Upanishads etc. 

This would be a more subtle view of the Ultimate than simple theism/atheism. I would agree with your Egyptologist in respect of the view expressed by this text.

It is a view that appears to be almost unknown in the Academy albeit there are prominent counter-examples. It is, after all, a competing product. The writings of Thomas MacFarlane might be a good reference.

It is not often noticed by religious sceptics that the God of monotheism is denied by a large part of religion, even though it is made perfectly clear in the literature. Religion has all the best arguments against God.