As for whether or not you can use this in a signal handler... well, I hate reading the POSIX standard with regard to signal safety because it's just not well-written, but as far as I can tell, a non-async-signal-safe function can be safely called from a signal handler for a synchronous signal (which most of the interesting signals for dumping stack traces are--it's only something like dump-stack-trace-on-SIGUSR1 that's actually going to be an asynchronous signal), so long as it is not interrupting a non-async-signal-safe function. So as long as you're not crashing in libc, it should be kosher.
As for whether or not you can use this in a signal handler... well, I hate reading the POSIX standard with regard to signal safety because it's just not well-written, but as far as I can tell, a non-async-signal-safe function can be safely called from a signal handler for a synchronous signal (which most of the interesting signals for dumping stack traces are--it's only something like dump-stack-trace-on-SIGUSR1 that's actually going to be an asynchronous signal), so long as it is not interrupting a non-async-signal-safe function. So as long as you're not crashing in libc, it should be kosher.