Depends how you make it look like. If you make it look like a blog project or freehost it should be allright to have tons of subdomains and pages that all get indexed.
We have freehosts where users get
http://subdomain.domain.com/ and all their pages get indexed and all get their own pr.
And we also have a blog system where users get
http://theirname.blogdomain.com/ and also all their pages get indexed, and spidered very frequently (most blogs at least once a week).
All subdomains are on the same IP, so it can work, but probably it helps if you make it look like it's a blog network or freehost?