You need a certificate for each domainname on each machine doing SSL.
IPs have nothing to do with it. If you have one SSL accelarator box,
it's a certificate for each domainname.
Very true the only thing an SSL box saves you is:
a) You only need to maintain one certificate (although its not hard to
copy and paste to 50 servers)
b) Possible licence issues with verisign and multiple certs, but I think
they've reworded it to screw you both ways these days.
As for performance I find it hard to believe a single SSL accelerator
could outperform 50*web servers!