If they have gravekeeper priest (who acts as necrovalley)then no you shouldn't since its just going to get negated and people are going to cry(I run a gravekeeper deck irl so it behooves me to know the strengths and weaknesses of gks)
Neither. It treats the "field" as Necrovalley. (It doesn't change its own name, so it's still a Gravekeeper, importantly.) It obviously doesn't apply any of Necrovalley's effects, however.