You can install an SSL certificate on any webserver, but you'll be limited currently to one SSL site per IP address - the webserver doesn't see which URL the host is connecting to until after SSL handshake, so yes you could use one SSL cert but that would be the limit.
SNI is the future! However older browsers will not work with it, ie 6 (windows XP machines) wont be able to access the SSL, however the small number of uses still on <XP hopefully have saw sense and installed chrome or firefox
FYI.. SNI works with Linux apache and works with hosts using latest CPanel or Plesk. and if your looking at Windows hosting the server must be Windows 2012 or 2012 R2, and I the only windows CP i know of that works with SNI is Plesk 11.5+
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