Yes, this is the expected behavior. As long as you stay away from PSOS and any new 13 based functions that could be evaluated by server in field definitions or finds you should be fine with your proposed alternative approach.
I imagine FMI is being safe with this, but it'd be nice to distinguish between "Minimum version of Pro" & "Minimum version of Server".
In earlier v-revisions of 13 I had seen some CSS scrambling when a Server 12 hosted file was accessed via 13 client. It was however, only reproducable under specific circumstances, and I haven't seen it since the last update of FMP 13.
Aah, interesting -- even though it probably won't come back. Thanks Josh.
I only mentioned it because it can happen if someone with 13v1 opens the file because they didn't update to 13v3. But even then, unless the person is actually entering Layout mode and save a change, it should be fine.
I ran into this with a new file I installed on a client's server. All client machines were FM13 and I had used FM13 features so set that as the minimum version. The catch? Client is still using FMS12. The result? The file would not upload. The outcome? System is running with FM12 access allowed for the present, until we get around to upgrading to FMS13.