I would actually say that is in fact basically true.
LMS will not provide custom tunes based on products that are not theirs. That being said, you can run their tunes that are based on their products with another companies products. They just aren't going to guarantee the results or modify the tune if it's necessary.
That all being said, most things don't require a tune at all so it's not something that you need to focus too greatly on.
However, lets say you want a Snow meth kit, full stainless works exhaust, and Mdesign intake, etc. LMS is not the tuner you want to go with.