They actually have changed the language in the
DME FAQ to be much stronger than that. It now says:
So it's now clear that their policy is guests are not supposed to have their luggage transferred without also taking the DME bus. That said, the problem for Disney is that they don't have any way to enforce that policy and, in fact, their contract with MCO apparently requires them to collect and transport any bag that has a DME tag (during luggage service operating hours).
Does Disney want you to use DME as a luggage-only service? No
Do they have a policy that says you must use the bus to get luggage transfer service? Yes
In practical terms, can you use DME only for luggage transfers? Yes
Will your bags get to your resort room if you tag them and don't take the bus? Probably
What each individual needs to decide (over and above their general views on following or not following rules) is if the "probably" represents enough of a risk.