Using Ultimarc's Servostik, LED Blinky, Hyperspin and Rocketlauncher:
So, Pac-man (and Puckman) were playing in 8-way mode on my servostik. In LED Blinky, I had noticed the controls were set to CONTROL_JOY4WAY, but the "Primary Controls" box was not checked.
Checking that box solved the issue.
That solution was not intuitive to me, so I figured I'd post it in case anyone else ever comes across that issue and searches for a solution.