I think you've brought up a very relevant and serious question when approaching any study of the thought of Will Durant. Durant was masterful in threading his own views, critical and philosophical, into all of his writings about history, events, people, etc., but it sometimes is difficult to separate Durant the Critic and individual, from Durant the serious, and well-reasoned philosopher (in his ending comments in the Reformation volume concerning Calvinism are extremely harsh; in summing up Calvin, Calvinism, and the historical legacy of Calvinism, Durant pans Calvin's conception of Original Sin as little short of an abomination of the gentle virtue of Christ - I don't have the volume at hand, but if I remember correctly, he insinuates that Calvinism’s doctrine of Original Sin has been one of the worst and most destructive ideas in the history of the West).
I think your point about Durant’s thought regarding Eastern philosophy is difficult to judge, mostly because the amount of good scholarship about Indian and Chinese philosophy during Durant’s college years (and up through …Oriental Heritage) was extremely scarce and often spotty and sketchy, while the scholarship towards the end of his life was fantastic in quality and breadth.
My short answer to your query is yes, I do believe Durant believed in a thing called “Eastern philosophy”, but I do not believe he understood it very well, nor was he aware of a great deal of it.
As a scholar in training in Indian thought (Mahabharata and Ramayana) I’m very interested in this question (Durant was the one who brought me into the fold of learning and academics, and I believe he deserves to be seriously studied) and if you are interested in discussing it further and perhaps attempting to write a small academic paper on the subject, email me, and we can start reading and picking out the good doctors ideas n detail.