Other than they'll eat anything fish or invert-wise that can fit into their mouth, they aren't usually a problem.
I've got one that's about 2' long in the 1000. He came from a 225 FO when he outgrew the client's tank. He has not bothered hermit crabs (large ones that were also 'donated'

) I've also got a Bahama Star and a really big
Chocolate Chip Star that were also 'gifts'... my 1000 g is a last stop for stuff that people can't take care of anymore

By the time that grouper is finished growing, it will likely be 3' long.
So to answer your question - yes you could keep one in a reef as long as you don't have small shrimp or bite-sized fishes (BTW my grouper ate an 8"
lunare wrasse much to my surprise!), but please please have an exit plan for this fish when it gets too big. Make sure your LFS is willing/able to trade it back in unless you have definite plans to buy a much larger tank.
HTH
Jenn
__________________
Member of the "J" Crowd & the BRW Crowd!
LFS Owner:
Imagine Ocean

Just keep skimming, just keep skimming, just keep skimming, skimming skimming! What do we do? We skim, skim, skim!