I believe that any socket based stream will take the timeout enforced by the default_socket_timeout, but offhand I've never tried this so I cannot verify.
Ah, here's a list of them too: http://php.net/manual/en/transports.php
So, I believe if you have set up a stream using any of the layers used in the above link, that those are all considered to be socketed streams and will take the default_socket_timeout. If not, they will of course be terminated by your max execution time instead.
This smells like something that needs a test. Sadly, the api isn't overly clear about this (or could just be listed where I wouldn't think to look :P).