You'd probably need a satellite meter (a real one, not one of those $20 "satellite finders".
A non SWM splitter doesn't actually matter. I did some tests using cheap cable splitters and I could hang a half dozen of them in series off a SWM output and still get good signal at a receiver over 50+ feet of cable.
If you have something that's on the margins of the spec in terms of length of coax run and number of splits an "extra" splitter could push you over the edge, but it won't really matter much whether that extra splitter is a SWM splitter or a cable/antenna splitter.
