You should have no problems running your 8.0 backups on a 8.1 system. The main change implemented by the upgrade to 8.1 was for Licensing. Make sure that you carefully read the 8.1 Installation and Licensing Guide before starting the upgrade, and that you have stopped, DP, made a copy of the 8.0 IDB, and the Configuration files (you didn't state what the OS-version and type your cell maanger is running on, so, I can't be more specific) and restart DP
Best peice of advice I can give you,plan on the Upgrade failing so you can easily roll back