There is an opinion that messianic Lubavitchers are complete apikorsim, which is that of rav menasheh klein in a teshuva.
From what I’ve seen he’s the only posek I’ve seen who says that; rav belsky said that they’re just meshugoim, and that one shouldn’t rely on them due to mental incompetence, but not that they are pasul for anything due to their beliefs.
Elohisten, including those who believe in god-in-a-body ideology, however, are ovdei avodah zara and are pasul for everything. Indeed, he told me that the OU checks every Lubavitcher shochet to see if they are in this category.