Altough it doesn't make a difference botting in US servers from EU, i don't recommend it! The game seems too laggy to be playable... (i know because i tried it, from 40ms it changed to 200ms+)
Though on streams, people can evne play high lvl pvp with the 200 ms so botting (llving and gathering) shouldn't be a problem I think, shame the battlechest action has ended now though
As long as you dont look into raid performance botting from EU is perfectly fine.. My latency is 350-400 Ms and i do current content heroic raids.. so just go ahead