Yes, you can add each frequency to the system as a different site.
However, there could be a couple of problems.
1. The 436 will not show the frequency, when programmed like this. To get around this I tag mine with the frequency then a short name. That way I will see what frequency was actually active, and some idea of the potential user.
2. If the frequency turns out to be capacity plus, and you have delay on, the radio may not leave that frequency. The active channel on a capacity plus system will put out a data burst roughly every second. If you see CAP flashing, you will need to disable the delay on that freq or avoid it.
3. My experience has been that I miss a lot of traffic when programmed as DMR one frequency, as compared to conventional and leaving the Audio Option set on search. I have tinkered with a lot of settings, and not found a solution to this. In fact, a local high school has a home game tonight, so I will be trying some more setting changes.
If these are truly unknown, I personally would program as conventional. With a little more effort of adding the default channel name via the radio, you will get the frequency and all DMR information. If it is Capacity plus, the same issue as above will be seen. You will also receive them, if they turn out not to be using DMR at this point.