If your procmail is limited to pattern matching and other built in functionality it is very likely that it will continue to work as expected. However, if you shell out to external programs it is possible that those programs may or may not work or even be present on the new servers. There was a substantial OS upgrade behind the scenes and given the flexibility of procmail it is impossible for us to test compatibility.
It is not practical for us to setup a system that would allow users to test their procmail rules in advance of the move. If you are concerned that your rules may run run afoul of the upgrade the best thing to do is temporarily disable them until we've completed the upgrade and you can test them in a controlled fashion.
The only other issue of note is that the upgrade will result in all vacation/auto-response databases being reset, the only affect being that remote senders may receive another auto-response before they normally would have if the databases were not reset.