We've walked directly down Harbor, as well as taken the shuttle to the walk in parking lot entrance on Katella. The shuttle seems to cut the distance significantly, but the walk seemed to take about the same time because the hotel entrance is on the end of the hotel closest to Katella. We didn't try to enter the doors of the hotel closest to the walk in gate, although our room keys would likely have unlocked the door.
I've stayed at the Desert Palms twice, and would recommend it (if you don't mind the walk). Loved having the 7-11 next door to pick up waters, sodas and healthy snacks (bagels, yogurt, etc). The free breakfast was your basic cereal, toast, fruit, and donuts. The rooms were clean, beds slightly on the firm side. Mini fridge in the room was one of the taller ones that will hold the taller water & soda bottles. Both times we stayed, we got upgraded to suites from the standard rooms for no charge. In the bigger suite, there is a full size fridge, etc. Front desk was very nice, and quite helpful. If you book through expedia, etc. make sure you bring your confirmation print out as we've seen those reservations seem harder for them to locate on check in than the ones you book with them directly.
