The only thing stopping you from having multiple OnLive accounts is the bandwidth of your home Internet connection.
One account playing a game in HD resolution requires 4-5 Mbps of download bandwidth. If you want to play on two accounts at once (both in HD), you'll need to have at least 8-10 Mbps of download bandwidth. Three accounts playing simultaneously in HD would require 12-15 Mbps, etc.
If you don't have plans to use both accounts simultaneously, you don't need to worry about having extra bandwidth.
If you've tried multiple accounts during the beta, share your experience below!