According to mt-st's man page, datcompression is supported
but it doesn't work, while GNU mt (from Debian) supports it.

moremagic:~# mt -v
mt-st v. 0.5b
moremagic:~# mt datcompression
mt: unknown command "datcompression"
usage: mt [-v] [-h] [ -f device ] command [ count ]
commands: weof, wset, eof, fsf, fsfm, bsf, bsfm, fsr, bsr,
fss, bss, rewind,
          offline, rewoffl, retension, eod, seod, seek,
tell, status,
          erase, setblk, lock, unlock, load, compression,
setdensity,
          drvbuffer, stwrthreshold, stoptions, stsetoptions,
stclearoptions,
          defblksize, defdensity, defdrvbuffer,
defcompression, densities,
          setpartition, mkpartition, partseek, asf.
moremagic:~# mt.new --version
GNU mt version 2.4.2
moremagic:~# mt.new datcompression 1
Compression on.