Arch Linux

It does depend on lesstif, check the namcap output.

look
$ ldd /usr/bin/xlock
linux-gate.so.1 => (0xffffe000)
libSM.so.6 => /usr/lib/libSM.so.6 (0xb7f4e000)
libICE.so.6 => /usr/lib/libICE.so.6 (0xb7f36000)
libXmu.so.6 => /usr/lib/libXmu.so.6 (0xb7f20000)
libXpm.so.4 => /usr/lib/libXpm.so.4 (0xb7f0a000)
libttf.so.2 => /usr/lib/libttf.so.2 (0xb7ee3000)
libfreetype.so.6 => /usr/lib/libfreetype.so.6 (0xb7e77000)
libGL.so.1 => /usr/lib/libGL.so.1 (0xb7e16000)
libGLU.so.1 => /usr/lib/libGLU.so.1 (0xb7d9d000)
libesd.so.0 => /usr/lib/libesd.so.0 (0xb7d93000)
libaudiofile.so.0 => /usr/lib/libaudiofile.so.0 (0xb7d6e000)
libasound.so.2 => /usr/lib/libasound.so.2 (0xb7cac000)
libcrypt.so.1 => /lib/libcrypt.so.1 (0xb7c7e000)
libX11.so.6 => /usr/lib/libX11.so.6 (0xb7b8f000)
libXext.so.6 => /usr/lib/libXext.so.6 (0xb7b81000)
libm.so.6 => /lib/tls/libm.so.6 (0xb7b5c000)
libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0xb7a82000)
libgcc_s.so.1 => /usr/lib/libgcc_s.so.1 (0xb7a77000)
libc.so.6 => /lib/tls/libc.so.6 (0xb795d000)
libXt.so.6 => /usr/lib/libXt.so.6 (0xb790c000)
libz.so.1 => /usr/lib/libz.so.1 (0xb78fa000)
libXxf86vm.so.1 => /usr/lib/libXxf86vm.so.1 (0xb78f5000)
libpthread.so.0 => /lib/tls/libpthread.so.0 (0xb78e3000)
libdl.so.2 => /lib/libdl.so.2 (0xb78df000)
libdrm.so.2 => /usr/lib/libdrm.so.2 (0xb78d8000)
libXau.so.6 => /usr/lib/libXau.so.6 (0xb78d4000)
libXdmcp.so.6 => /usr/lib/libXdmcp.so.6 (0xb78cf000)
/lib/ld-linux.so.2 (0xb7f63000)

Maybe some of screensavers depends on it, but without it xlock works fine.
I think that it will be okay if you just mention this library in Description.
In debian such things writes to Recomends field.

xlockmore comes with a motif GUI, which requires lesstif.

oh, sorry. Found me fault. lesstif is required by xmlock application which comes in this package.

Sorry. You can close this bug.