I would definitely disagree with this:
It does not help you tackle the inference, author's intent kind of questions which is more frequent in GMAT
LSAT RC, especially from preptests numbered 30 and higher have a very high concentration of inference, logic function, parallelism questions etc. I teach both tests, and I can tell you that the hardest LSAT RC is definitely harder than the hardest GMAT RC.
That said, there are important differences between the two tests. A tough GMAT RC passage is likely to be quite technical while the wording is often quite straightforward. Conversely, a tough LSAT RC typically isn't highly technical but will be highly abstract with very dense and sophisticated academic prose.
Can working on LSAT RC help you?
Most likely, yes.
But I still think it is better to practice on official GMAT questions.
Can GRE passages help you? I've seen some good ones. But I don't teach GRE on a regular basis, so I will refrain from commenting about that other than to reiterate that your interests are best served practicing with GMAT materials.