Trunked DMR have priority option for TGs but not on one frequency systems which have the priority greyed out on the main page and are not visible at all in the edit system page.
One frequency systems normally have one slot for controldata and one for voice, no need for priority, and there are Hytera XPT channels that can have voice conversations on both slots, but it might not be a feature worth the hassle to develope only for those channels.
I have several DMR channels I check for if they ever get active with traffic or might have moved to other frequencies. I have them entered as plain analog conventional and as priority in a special system so I can choose to scan them or not. If they have DMR signalling it will automaticly be decoded and audio monitored.
But you want to check only slot one and disregard what's happening on slot two, then I cannot see any solution for that.