snipers are nice anti crab yeah.. but..

spider has the best non napalm anti sniper decloaker in the game (flea)

crabs can sit on the back face angle of the top of the spire so they can only be hit from the sides by snipers.. allowing them to force the snipers in closer.. and the crab still gets a quite nice fire angle over the tip of the spire

widdow can sometimes scout snipers too and if you place it on fire at will they will often emp sniper before it can shoot.. but again mass flea is better and is the true answer.

if enemy counters you with lotus or pickets then recluse + flea will work unless the snipers micro to kill the recluse =/

if you cant flea then switch into something that can handle sniper like firewalker.. unless they have shields.. snipers + shields + mass lotus is really op vs everything except a major assault, surgical strike (cloaked snitch, tac missile, merlin, cerb, bertha.. ect) or air

oh another thing i forgot to mention.. sparrow.. i know it costs metal but 1 sparrow can allow a crab to make cost vs snipers even naked ontop of the spire

and limpets + ducks are great vs snipers and can handle lotus but its a bit more expencive.. mainly useful because of area slow

Traps:

imps emp eachother and are not so good at flushing snipers but can lay traps.. blastwings can flush but chain allot.. they also should make nice traps on 'land' and cloaked but like imp its hard to set up

badger is godly vs snipers.. but wont do well vs napalm (firewalker, pheonix) and shields.. and has poor dps if enemy switches to assault units

Seige:

tremmor is expensive and tends to get sniped unless you dig it but can defeat shields

slow tac.. this missile is really underated vs slow reload units.. turning 10 snipers into 5 for a long time.. aswell as allowing a charging force to reach them and engauge before they can run.. but its expencive so its one of the more risky tactics.. mostly good vs shield balls as it doubles recharge times.

Napalm:

pheonix can annihalate snipers once you find them unless shields

inferno is the same as pheonix once they have shields its useless without emp

there are probably heaps of others i missed
also you know all this already because your purple rank =D