Generally speaking, tags aren't created until there is at least one question to add it to. (It's a feature of the system; you can't create a tag in a vacuum. There has to be a question where those with enough reputation can add the tag.)
While someone has gone and created the tag here, both of the questions you cite seem to be development questions, not web app usage questions. I suppose that for an app like yours that might be a fine line. Part of what makes Stack Exchange successful is the robust community moderation. Stuff that's off-topic gets closed and swept away, keeping the quality of what remains high, which attracts experts to answer questions, which keeps the content of high quality, and so on, in an infinite feedback loop. Unfortunately, if you shunt all of your support questions over to Stack Exchange, your users may not be used to the sort of moderation that occurs here. Further, there will be plenty of questions from your users that would not be appropriate on any Stack Exchange site. Questions that can only be answered by CommCare personnel, for instance, or which are so specific to one person that they can never be useful to anyone else.
It's also not unheard of for an app to be covered by multiple Stack Exchange sites. Dropbox, for instance, has a web interface, and questions about that are on-topic here. But the synchronization app that automatically synchronizes your files from your PC to and from the cloud is off-topic here. Questions about that belong on Super User. Similarly, questions about the Android and iOS Dropbox apps are off-topic here.
So, sure, general access/configuration kind of questions about CommCare will probably do all right here, and questions that are specific to development on CommCare will probably do fine and Stack Overflow. But if the questions you linked to are what we should expect, I don't think anyone is going to be happy.
I suggest that before you fully implement this, you check on some of the advice offered at Meta Stack Exchange and Meta Stack Overflow for people who have already done this sort of thing. (Is it okay to use Stack Overflow as the support forum for a product or project? is a good place to start, and the questions linked to it.) Not to mention the advice in the Stack Overflow Help Center. I'd also suggest you contact the Stack Exchange team for specific advice. You can reach them by using the "contact us" link at the bottom of any Stack Exchange site.