I often find it hard to drawn any real differences between Taoism and Buddhism. Because these two have historically influenced each other, should Taoism be allowed as a subject for discussion on the Buddhism S.O.?
I'd say no, unless you are comparing/contrasting the two, or looking into influences etc.
Stackexchange is not a platform for discussion. "Question & answers" is the communication-form for which this software was developed. If you have a concrete question, and if it is somehow related to buddhism, and this relation is also relevant, then -for instance- I am much interested to look at it and to say what I know. For the "discussion" of Taoism I think I'd try to look at facebook or usenet. Possibly the stackexchange-people are currently developing a discussion-orientated software, but I've not yet a real impression of this, so if you want to attach you to this you likely have to wait a short more time.
We have taoism which gives a good idea of the type of questions that work but they always relate to Buddhism in some way.
Personally I'm not convinced they are similar enough to be interchangeable on this site. For instance Taoism had a big thing going on about immortality which is completely at odds with Buddhism philosophy (IMO). That said if you disagree with that statement then there would be a very reasonable question for the main site.