I use an internal LTO3 in an ML370 G5 and an external LTO3 in an DL370 G6 connected via an SC44Ge host bus adapter. Both work OK (ESXi 4.1 Update 2) with the notable exception of asking for the drive status (mt status command from a linux guest) when there is no tape. In this case the host repeatedly loops, generating NMP error messages. The only way I've found to stop the errors is to put a tape in the drive. Obviously, this is OK so long as you're vigilant about changing the tapes but it's far from ideal.