Yeah, swap appears to be working just fine.
But, it's really looking like the problem is simply that Linux is using up too much system RAM with cache, resulting in unecessary swap usage.
That is, I think what's happening is it's getting within about 5MB of my total RAM (which is probably far too low, considering the RAM is almost certainly highly fragmented...), and when UT's RAM requirements change a bit mid-game, I get massive stalls.
After reexamining the memory usage, though, I should have plenty. It would be nice if I could find a variable that I could modify to reduce the amount of RAM that the cache will attempt to use, and see if that fixes the stuttering problems.