There's a big difference between me running a filter on other people's words, and those people themselves choosing to run one and then approving the results.

I personally don't see a problem with someone using a grammar checker as long as they aren't just blindly accepting its suggestions. That said, if someone actually is using it in that way, it shouldn't be detectable anyway, so it probably doesn't matter all that much whether or not it's included in the letter of the rule.