Though there is no written rule that we have to, almost every 10th Planet will let a member of another 10th Planet drop in for free. I have been to a large number of 10th Planet schools, including prior to me running a gym and the VAST majority wouldn't accept payment for my drop in since I represented 10th Planet so I bought gear or got a private lesson with the coach. Jiu-jitsu in general has a great community and I feel like the 10th Planet community is that X 10 at least. Though its best to call ahead in this case, your extremely likely to be able to get a free drop at another moon, yes.
And I'll also mention, from experience, that if your acting with respect and show people your 10th Planet for life and trying to not just take but contribute however you can, that the amount of help and benefits that could be available to you might be FAR FAR more than a free drop in at a moon. We call it the 10th Planet "Family" for a reason, and while you definitely shouldn't go places feeling entitled to other peoples generosity, often you'll be treated like a real family member in regards to anything you may need. The people here are the best reason to become a part of 10th planet.