I see lots of scrappers and holos on my server, less frequent than firebrands or scourges for sure, but definitely not the rarest. Scrappers definitely get a lot of love, people do appreciate what they bring to a zerg. My server is pretty high pop, so roamers are a lot rarer, I roam with a havoc group from my guild from time to time. The truth is, regardless of class, your not very useful when your by yourself in WvW. You can basically flip camps and kill dolyaks, which you could do easily with rocket boots and grenades.