Chris,
Hi, it's Joe with Dell EqualLogic. You should be able to use various vendor DSM's on the same host. The EqualLogic DSM's are optional.
The EqualLogic DSM does offer enhanced features that the native Microsoft iSCSI initiator DSM currently doesn't offer. Most notably in the MPIO module. Normally with the native DSM, you need to login to each iSCSI interface that is part of the multi-path (i.e., INT_iSCSI_0, INT_iSCSI_1, etc.) one at a time. With the EqualLogic DSM, you first identify the iSCSI subnet you want to use for the connections, then login to the first interface, and the rest of the interfaces in the iSCSI SAN subnet will "automatically" connect the remainder of the interfaces.
Regards,
Joe