It's the first I've heard of it, and sounds to me like an attempt of fannish retconning, trying to position TNG as "real" Star Trek at the expense of anything else.
Memory Alpha makes no mention in its Background or Apocryphal sections that "God" and the Cytherians might be related.
Why can't "God" simply be an alien species never before seen or afterwards? Why does everything have to be connected?
TNG is just as 'real' as the other Star Treks. Everything doesn't have to be related, but that doesn't mean that some things couldn't be related. Plus, the Cytherians and this being from Star Trek V look remarkably similar.