Hopefully someone with hands-on experience will comment for you, but all I can say is that it might be a bad idea or it might be fine. Personally, for the reasons discussed below, I would guess it would be fine, but I'd probably test it by adding an urchin to a test tank with the shrimp before adding them to the display.
I haven't really looked in depth on these guys before, but - researching them a little now - it seems it's unconfirmed to science if these guys actually prey on echinoderms or not (the few pics/videos I can find of them "preying" on starfish show them crawling along on the feet of the stars, but no damage seems to actually be done so I can't even confirm using hobbyist info if they actually prey on echinoderms or not). However, based on their mandibles, it seems somewhat unlikely that they do. Rather, it's suspected that they feed on mucus produced by the echinoderms or on particular organic matter trapped in the mucus instead of the echinoderm itself. There is speculation that these guys only feed on the tube feet of echinoderms (much like how Harlequin Shrimp are rumored to only eat the tube feet and not the whole starfish), but I suspect that - like with Harlequin Shrimp - that is untrue. From what I've seen/read, I'd guess that they more likely are trying to eat something else (such as mucus) by the tube feet rather than the tube feet themselves (though it wouldn't surprise me if they occasionally got a tube foot or two in the process).
Harlequin Shrimp (who, notably, have different mandibular structure) eat the entire starfish (though they generally, to my understanding, start with the tube feet - likely to prevent the star from escaping, but possibly for taste), and - unless someone has evidence to the contrary - I'm starting to suspect that Bumblebee Shrimp may not eat echinoderms at all. They do, however, seem to be pretty aggressive in getting at the tube feet of sea stars, and they do exhibit a feeding behavior (though again, I can't see any signs of damage being done by the feeding).
The hunt is on! My bumble bee shrimp loves to hunt this guy down. He will post up on the rock behind, drop off spiderman style and then go in for the kill. I think he only eats a few pieces and then books it. Yesterday he went in big and I was able to snap some pictures for once. By far some of m...
www.nano-reef.com
(The link above has pics of a Bumbleebee Shrimp "attacking" a Sand Sifting Starfish - no noticeable damage is done despite the shrimp visibly holding/"eating" the tube feet; it's possible that damage is done that's just not shown in the pics, but I can't say for sure.)
Also, from what I've read, only Bumblebee Shrimp (
Gnathophyllum americanum) from Florida are reported to live commensally with urchins (specifically
Lytechinus variegatus, the Variegated Urchin; these are sometimes called the Green Urchin, but that name is more commonly used for
Strongylocentrotus droebachiensis, which is a coldwater species). I don't know if they will live in the spines of any urchin, or if it has to be that specific species (and I don't know how strong of a commensal relationship it is between the shrimp and the urchin in either case). Regardless, because of the speculation that Bumblebee Shrimp feed on echinoderm tube feet, there is speculation that they live with these to occasionally feed on their feet, but there is no confirmation of this idea that I can find.
So, again, personally, I'd probably give it a test run by feeding the shrimp in a separate tank, then adding an urchin to the tank to see how they do with it. Don't be surprised if they charge the urchin to get at its feet - what you really want to watch for is if they do any damage to the feet/urchin (such as if they actually eat the feet, or if they just grasp them and release them after messing around with them). If there doesn't seem to be any damage done after like a week, I'd guess you're in the clear to add them safely to the DT.
If you try it, let me know how it goes.
*Mandible info:
