We are currently doing it.  We actually have three machines using our 3494.
Initially we had two drives on one machine and 10 on the other so we varied
off on the 10 machine the two that the other was using.  Now we have both
with 10 drives so they just use the drives they need.  Machine A will not
use a drive if Machine B is using it.  It marks the drive unavailable and
then starts polling.  We don't have it set up as a shared resource.  You
need to be careful that you don't ever lose your 3494 library's database
because then when you do a checkin search=yes the result is unpredictable.
Keep an eye on who is using what tapes so that both machines aren't thinking
that a particular tape is theirs.
Good Luck