The one has nothing to do with the other. I'm a big fan of microkernels but this class of bugs has nothing to do with whether or not you use a micro kernel or a monolithic one.
That's not true, it strongly affects the ability to separate privileges and apply sandboxing. For example, compare Apple's Seatbelt, which was a comparatively light lift to the intrusiveness of SELinux or restricted token sandboxing on Windows.
If by class of bugs you mean "munging the stack," yes - but the difference is in the effect on integrity of the total system. In monolithic kernels, if an attacker can monopolize on the situation (by defeating mitigations, if any) and control execution-flow, they can run code on ring 0. This isn't the case if you're on a microkernel where a bluetooth driver lives in userspace.