If I really wanted to, I could come up with dozens of different roles that require empire arial thief to hoard good-only limited items and requires him to full sac every corpse he comes across, or come up with a dozen different roles for an elf transmuter to carry around dozens of evil-only limited items while duo'ed, and never let him stay out of duo for more than 30 seconds.

Its still lame and powergamey as heck.

If you were really creative, you could justify any IC action with the right set of roles. ELF AND DUERGAR SINGS JINGLE BELLS SIDE BY SIDE BECAUSE THEY BOTH LIKE KILLING MAGES LOLOLOL. Best to make the lines clear as to what is acceptable, and this line feels pretty obvious to me. It is acceptable for an elf and a duergar in the village not to kill each other on sight, but it is not acceptable for them to go hunting shinies together or killing mobs in a group together.