Yes, from a context viewpoint, but there are at least two other ways to look at it:
The Absolute isn't a deity, despite what its followers think. There's a bit of dialog with Dror Ragzlin while he is trying to resurrect the mindflayer that shows what the Absolute is.
So you aren't betraying your god for another; it's more like joining a rather restrictive club.
It doesn't actually restrict your actions, e.g., you can still kill Absolute followers and do things your god wants. So it's a meaningless oath.