Well, yeah!
Looking into this a little bit, I found that a proposed J-2T was designed with an aerospike nozzle, which obviously means that it was designed for use with atmospheric pressure. The J-2X has no need of that, so a test stand built specifically for sea-level conditions is useless. I wonder if this test stand is being built just in case they decide to revive the J-2T program, but using the fuzzy justification of the J-2X requirements for the Ares program. I suppose a rocket built with just J-2Ts and J-2Xs would be pretty cheap for space probes and such.
It’s pork for Mississippi. Stennis already has plenty of rocket engine test stands that would work just fine with modification. So does Redstone/MSFC in Huntsville, AL.