Yes, it will fruit as long as its pollinated. But you probably won't like the fruit you get! It'll probably be nasty, small, and sour as all heck.

The rootstock is selected only for the root vigor not the fruit. It's most likely M-111 rootstock as most people that graft apple trees use that. I have some M-111 growing as rootstock but I have never let it grow to fruiting size before I grafted something to it. You could try your luck at grafting in the spring since you have the rootstock growing. You have plenty of time to read up on how to do it since spring is almost a year away.

Lou