All of mine are fresh water - I would love to have a marine invert setup as they are so much more colourful.
I first tried some amano/glass shrimp in my community tank but they quickly disappeared. It may be that they are still in there but are very good at hiding but I think it is more likely that they became food.
Next was the big armoured shrimp which is in my largest tank and is too big to get eaten but he tends to stay in his own little spot all the time anyway.
I have now a small tank with a few amano/glass shrimp in it (from two different sources) and three long arms - no fish. I might be moving a couple of the long arms to my 'small fish' community tank at a later date as I think they are getting too big for the small tank.
I think your clown loaches would think 'Yum, Yum' and I doubt that the crabs would appreciate the competition for floor space......
Cheers, Eddie