Yes, it sounds like your understanding is correct. If you know the time of a specific PPS, and you know what I/Q sample it occurs on (information that our API provides), you can extrapolate timing to any sample. The PPS will appear in the I/Q stream each second, so you can continually correct for any drift/error.
The main advantage of using the internal ublox-m8 is convenience. In a multi receiver setup such as yours, what approach you take will likely depend on your timing requirements and/or hardware limitations (i.e. can you run 10M/PPS to every receiver).
The ext trigger example I mentioned can be found in the SDK, in the sm_series/windows/examples/c++ folder. It only shows you how to call the functions, it does not simulate timestamping. Programming specific questions are best directed to me via email, or if you need a more elaborate example.
Andrew
