KeepItMobile,
It's not so much a quesiton of safety, its a question of performance. We allow up to 8 members in an ArubaStack however the stack links are only 1G so if you have a lot of inter-stack traffic, this can become a bottleneck. The same is true is you only have a single uplink off of one member, it would mean that all user traffic from the other members would have to cross the 1G stack links to get to the uplink.
Best regards,
Madani