Ummm.... I've been working with PHP for 16 years, and I could count the number of coredumps I've had in production on one hand (maybe 2). Early on, when compiling extensions by hand, I'd get some when I compiled something wrong, but that was always in test areas on dev machines.
If 'core dumps' were 'a common issue', I doubt it would be as widely used as it is now.
We were typically getting up to 200 req/second on our stack. So it was pretty heavy traffic to begin with. We solved the core dumps though. And the java core dumps were for the same reason (necessary to connect to JNI).
And yeah, connecting to C libs is commonplace in large PHP places. In fact, that's how PHP gets a lot of it's work done to be quick. Your ".01%" is a number you're throwing out of your ass and you know it.
I'm not surveying PHP usage, merely telling my experience. If you work on a website and need to connect to an external system that only has a C lib, guess what? You're going to connect using C libs.