App submissions tend to be about the code submitted, not the OS that generated it. XCode is the focus here and the store rejects any code that comes from Beta XCode version (having done that by mistake more than once,). Im not sure they care about the OS part, as it doesnt leave trails in the code that seem to care about. Today you can submit on a range of OS X versions, basically anything that runs XCode 6.x and meets the other code requriements.
In the past they have always had both a GM version of XCode for each OS beta, to support submissions and other testing. With XCode7, I have not seen the normal words about no submittal using the beta that normally is there. Maybe its there and I just missed it. Do we know for sure that current XCode7 cant be used for submission?