I plan on getting a Yellow Watchman gobby for my 25 gallon mixed reef tank with a refugium int he sump. But should I "spot feed" him or will he find food for himself?
If competition is fierce you might do well to spot feed him for a while. Mine competes well for food even with a bunch of very boisterous, active feeders. Mine eats almost anything but loves LRS and Hikari mysis the best.
The YWG will definitely need access to a meaty food source outside of what is in a 'fuge. Go with LRS Reef Frenzy, less gross filler material going in your tank and it's a good all around food source (corals, inverts, and fish). It's an all in one diversified omnivore diet (heck even my Yellow Tang and One Spot Foxface, which were supposedly dedicated herbivores loved it). Here is what it has in one food source: