My personal thoughts (and experience):
"Was programming/computer science brought up in your undergraduate/graduate mathematics education?" - yes, but I took math+CS+physics for my undergrad. This isn't very rare though; at least in my time (and place), most math majors took some CS (If nothing else, there's a big overlap in the required courses). My feeling is that most mathematicians of the younger generation have at least beginner-level programming skills, but my view could be biased. Of course being able to program could be useful for doing certain types of math research; for other types, it's not really useful at all.
"Did you see any consistent problems..." - I don't think so, and in fact I believe that for people who have solid math background, learning the fundamental skills necessary for programming is relatively easy.
I don't know what "metacognitive" means, but I feel that it's reasonable to expect that people who understand programming languages may have an easier time grasping certain kinds of mathematical definitions and points of view. For example, it may be useful to think of mathematical objects in an "Object-Oriented" way, thinking about what forms part of their data structure (and what doesn't) and what "methods" they expose.
It may also be useful to think about what it means to "calculate" something abstract (like the cohomology ring of a manifold) even when there is no real possibility of implementing the calculation; just reasoning about what it means to say that data X can be calculated for object Y can be useful. So here, too, a certain kind of CS-like training can be useful (and is increasingly common anyway).