Depends on how finicky the rider is, general brake setup performance, and rider hand strength.

For someone with full use of their hands and decent hand strength, the mismatch isn't any worse(rather better) than braking on steel rims, or braking in the wet, which people tend to do "all the time" w/o any disasters happening.
It's like with most things, you can afford one feature being substandard and still do OK. But if you get several things stacked up against you simultaneously, you're in trouble.