i guess its as safe as its ever gonna be...there aint no cross tolerance between the two substances as far as im aware...the first is an upper and the latter a downer so to speak...you might run into trouble combining the two together, however i have no doubt it would have been done before...
There are no risks associated with this, and even when the drugs are combined there are few special risks. It's not supposed to be very enjoyable though.
If it's small you're all good. although after i night of getting into shit like oxy i can't imagine i'd be in the shape/mood to want to roll the next day haha.