They can, but they might have trouble discovering it. Other instances won't become aware of your magazine until one of their users searches for it explicitly, and even then posts won't be federated until someone subscribes. So you've got some advertisement to do.
This is a general problem though which Lemmy suffers from too. Lemmy has this problem less because there's third-party websites which list all Lemmy communities and you can browse them there. But those don't support Mbin magazines from what I've seen.
One way to overcome this problem that I know of is Lemmy Federate. As I understand it, it tries to subscribe to your magazine from various instances (including big ones) using its own account, so it starts getting federated there.