The Marksmen set does 8% bonus damage toward enemy players. So I am wondering if the target dummy will be considered a player so that this set can be tested against others for pvp build?
My best guess is no. The same logic could be applied and we can ask if it counts as a dungeon mob so we can test dps with VO/IA sets, but it's probably not going to count for that either.
The minor slayer buff does apply to the target dummy based on my reading of dps tests in other posts on the forum. Don't know about the marksmen set bonus to players however. It feel like it couldn't, cause then people could get impractical numbers if they had marksmen and 3 piece VO slotted.