The signal system being used on the Crosstown is a Bombardier (now Alstom) product called Cityflo 650 on the tunneled sections, and (IIRC) Cityflo 350 on the surface portion. It's an off-the-shelf product that has been used in many, many different cities on many, many different lines, although the 650 - the fully automated one providing ATC/ATO - frequently on unmanned "people mover" type of systems. But this is by no means it's first transit application, not by a long shot.
As pointed out, Finch West is using a version of Hitachi's (formerly Thales) Seltrac product. It's a totally different system, although it is functionally identical to the Cityflo 350 product - and nothing at all like the version of Seltrac formerly used on the Scarborough RT.
Because the two systems are completely independent from the other, there should be no possibility of any failure in one propagating to the other. I say should, as I don't know how the scheduling functions have been integrated into the two systems. If they are centrally controlled - like the existing subway lines - than there remains a potential common failure mode there.
Except that the migration point between the two systems is not the problem. In fact, it's worked flawlessly since the last upgrade in August/September.
Dan