boar hit the nail on the head... snipers provide a huge boost at the cost of field presence. they can work at all levels, but their role changes as the number of players goes up. in 3s and 4s they tend to get forced to retreat more, so they're less of a manpower bleed tool than support against support weapons and blobbing. the OH sniper is particularly nice once it gets the incendiary round.
i have a buddy who would routinely use 2-3 snipers in 2v2s and was insanely good at managing it... but he had very good micro. i disagree with OP... i don't think you can just ignore the snipers, but you definitely have to work around them. they can't move quickly without exposing themselves, so you attack in other places to minimize their bleed.
