If the toms are hot & ready, they'll come a running. I've read in a few places that many hunters have slightly better success when calling to downhill toms. I hunt some pretty slanted terrain, but the last spring bird I harvested came downhill towards me.
I'd guess that good patterning of the the flock you're hunting should be a concern before worry too much about uphill vs downhill.
Get out there, and call to 'em. If they, they come. If they come in range, take 'em.
The turkeys have the PhD's and I'm just a dummy in the back row.