By way of follow-up:
We contacted Green Hope Lodge, where the manager, Pham, assured us he could get us 6AM boat rides across. So we stayed 5 nights at Green Hope Lodge, and one night at a room in the park HQ area. Green Hope Lodge worked out fine for us, as we were able to cross each AM at 6, and Pham always made sure we had tickets for the next day. We very much enjoyed Green Hope, and would urge other birders to consider it. We stayed one night within the park in the hopes of getting an early jeep to the Crocodile Lake trail, but they would not provide anything before 6:30. (BTW, I can confirm it is NOT necessary to pay the extra 140,000VND PP to use this trail if you can convince them you are not going all the way to Crocodile Lake.)
I was pleased with our birds at Cat Tien, which included Germain's Peacock-pheasant (best views 7-800M SOUTH from HQ toward grassland area), Green Peafowl (a few K further along this road, a little after the first building),Siamese Fireback (on road en route Crocodile L Trail), and both Pittas. The local guides have established a "pitta restaurant" for photographers, somewhere behind the "big tree" and back towards HQ area. We stumbled upon a Blue-rumped Pitta that actually allowed itself to be seen, and shortly after found an obvious photo setup where a Bar-bellied Pitta, not knowing we had no mealworms, came close.
We also had White-rumped Piculets, a Chestnut-winged Cuckoo that hung around HQ, and marvelous Gibbon concerts each AM. The restaurant in the park has an extensive menu but only a few items available, altho large Vietnamese groups who had apparently pre-ordered for Tet had quite elaborate meals.
We took a taxi from Cat Tien to the hiway (my wife doesn't do motorbikes) and then a bus to Di Linh. The bus fare included a minivan to our hotel, Juliets Villa Resort, a delightful place about 5k out of Di Linh on the road to the birding spot Deo Nui Sanh ( a name which no one at our hotel recognized). We took taxis to and from the tea shop. Birding was slow, with only flight views of Orange-breasted LT.
Bus was easy to Dalat, where we stayed at Villa Pink House, and just used ordinary taxis each day. But we definitely struggled with some Dalat specialities like Cutia. On the plus side, I'd love to go back to Dalat.
Thanks for your help Florian