as far as i know, there isn't. like, rsbots.net creates bots like tar picker uper, frog legs picker uper, you know, those things that pick up other things, haha. sounds funny.
but yea, maybe they might create a script that could possibly pick up grapes too, but you never know. the spawn might not respawn that fast so they don't take it into serious consideration. so yea, probably will never and wont be a grapes bot.