re OP
i think it is an EXCELLENT thought, and well done U, too! > click <
the dogs get a break from kennels, they can learn or refresh their in-home skills, and the care staff get a slight break from care + clean-up duties... plus Ur dogs can practice their dog-social-skills, never a bad thing!
i would only add the caveat that having Ur dogs meet the visitor OFF of their property, if possible at the shelter to ensure that they hit it off, is a good ice-breaker; introducing a complete stranger-k9 to the resident-dog in the living room is never a really good idea, LOL... it makes a bad impression of invasion, not a visit.
once they have had an on-leash (Ur dog) intro thru a fence, with the potential visitor off-leash inside the fence, U can then decide if they all want to get closer acquainted; this may save some bloodshed, LOL, or just keep the dogs calmer vs instantly popping off leashes and letting them go manic! ;--)
if their off-leash play at the shelter / tennis court / other fenced area is happy, i would say that U are good to go... but i would also CRATE the resident dogs for the trip home from the shelter, and harness the visitor to prevent walkabouts or falls in the car.
once U get there, have someone else take the resident dogs to the backyard, then preferably join them after another fence hello...
to refresh their memory, LOL. this gives the visiting dog time to potty before entering the house... in case the dogs standards for housetraining have slipped.
have fun, i think it will be a blast for all parties!
cheers,
--- terry