If your LR
is mature enough, and has enough biologic filtration...then any/all ammonia produced by the rotting shimp is being quickly/immediately converted to nitrite by the LR
bacteria. Same goes for the nitrite and even the nitrate.
So..yes it is possible. If the testing is reading zero levels, leave the shimp in there...they won't last for too long. Maybe add a hermit or two now...they'll polish of the remains of the shrimp.
Where did you get the LR
? If it arrived to you very fresh and unharmed, it likely became effective very quickly.
Even so....give it a week of reading all zero on the tests...just to be sure.