I went into the dungeon to tame the dino boss Rezan not realizing that it’s a BM only tame. I was MM spec, it let me tame Rezan and then Rezan disappeared from view but was in my list of pets. When I tried to summon him as an active pet he would start to appear but then disappear.
I went to tame a different pet (a dino in King’s Rest) and I did not have an active summon, but it wouldn’t let me tame anything because I had ‘an active summon’ but I couldn’t dismiss any pet because I didn’t have an active pet. I had to summon a different pet then dismiss it to get it all straightened out.
TLDR: you can tame Rezan in MM spec.