+/- isn't a good stat to judge much of anything, especially in a short time frame. The issue I have with him is that he's a small one dimensional offense only winger. Doesn't skate well, not physical, no defense.
The real issue is his linemates though. Sheahan and Andersson are softer that Persian kittens, Andersson has little skill and is at best an average skater, and Sheahan is looking like he's peaked. Give him a couple guys who are better skaters and Pulk wouldn't stick out as much.
Yeah, +/- isn't worth much. But he's a pretty good skater and his defense is no worse than Tatar or Nyquist. He's leading our team in takeaways, 3rd lowest Corsi against, and been on the ice for only 3 goals against, 2 of those being empty nets.
He hasn't been playing with Sheahan by the way. Andersson and Helm for a couple, then AA replacing Helm last game. He also played with Tatar and Larkin for a few games. Plenty of good skaters. Hasn't stuck with anyone for more than a few games.