I have had two MP10's in my seahorse tank for 4 yrs, and have used the foam covers with no issues.
If you don't turn the pumps off when feeding though, the mysis/brine will get sucked into the foam cover. No biggie if you change/rinse them frequently...
(One seahorse even used to let the "suction" of the MP10 to pull him onto the foam cover so that he could eat the mysis/brine shrimp caught in the foam cover. He would then swim off when he had his fill without incident!)
The same seahorse would also hitch to the front of the pump or the foam cover, in full blast of the flow. He seemed to enjoy the "spa". Go figure.