Last year there was a detailed discussion of watchdog timing:
https://ogrforum.com/...n-yard-tracks?page=1
To answer your specific question, the stock out-of-the-box DCSRC only generates a single watchdog about 1 sec after it initially receives power. The widgit discussed in the above thread is a modification to the DCSRC to make it continuously generate a watchdog about 1 per second as long as it is powered...hence the term Perpetual Barking Watchdog or PBW (not to be confused with PBR which is an alcoholic beverage). The PBW is more suited to a yard or intermittently powered sidetracks...as opposed to a mainline. The DCSRC has a "weaker" watchdog signal than a TIU as it was meant for DCS Starter Sets. Hence it would be a your-mileage-may-vary situation to reach and silence an engine on the far-side of a large layout.
In your hypothetical context, a TIU and a DCSRC (stock or PBW-modified) can co-exist on the same track. There might be the occasional data collision if both devices are talking at the same time but the DCS protocol "allows" for this situation and there would be no perceptible loss of performance except in rare or contrived situations.
