It is possible to set up Voting Scan for analog channels - I run it on a daily basis since our state police agency uses an analog multicast system. When configured correctly, it works just like roaming would on a digital system. That is, of course, provided you have the Conventional Voting Scan option enabled in your flashcode (assuming you do).
You cannot, however, have both analog and P25 channels in the same Voting Scan list as that will be marked invalid by CPS. I would advise creating two separate personalities, as it sounds to me like you might have analog and P25 in the same one. This will make things easier to configure.
Check out the attached screenshots from APX CPS which discuss valid field configurations if you haven't already. There's a lot to pay attention to, and it's important to remember that your personality, scan list, and zone/channel config must all align. Send a screenshot if you're still having trouble.

