No worries, Derek
If they are trying to remove mildew, the grout will cleanup nice with Clorox.
If we’re talking any other contaminate, Clorox will not do it. It's not a “cleaner”.
Bleach will not “eat” at the grout. In fact, it will not cause any structural damage whatsoever. It can cause discoloration on a colored grout. So the “clean” joint might look worse than the “dirty” joint.
What was the question?