How many midi channels on one midi 5-pin cable is reliable?

Yeah, people mix terms all the time.

I’ve seen a few devices that has MIDI and word clock or other sync protocols, e.g. SMPTE. These devices don’t mix data in any way, e.g. between MIDI and SMPTE, but rather makes sure the onboard protocols are synchronized properly and across devices.

Here are some additional resources on the sync topic Sweetwater and another forum HomeRecording.com.