It looks like the issue isn't with the Time::HiRes module, but with the glibc libraries which are part of the RH EL distro.
Directly using the usleep call in C on RH EL has the same issue. FC3 does not.
Fedora Core 3: glibc-2.3.4-2.fc3
RedHat EL 3: glibc-2.3.2-95.30