Thanks for pointing out the distinction. Unfortunately, I'm stuck with whatever build of Perl the operations staff compiles. We're currently on v5.10, which does have thread support built in, but if a future release comes along that omits it by default, I may be out of luck.
(http://perldoc.perl.org/perlpolicy.html#discouraged states that discouraged features are considered to be "mistakes" that may one day be deprecated.)