The PacLED64 and Ultimate I/O both manage the current at 20ma, so you shouldn't run into any issues with LEDs degrading.
FYI, the GGG RGB Drive II LEDs were actually 18ma max rated when I bought them 2 years ago, so even with a resistor the UIO (or PacLED64) will feed it 20ma and they will degrade over time.. I have several that are dim on certain colors, flicker in and out, and in general are working poorly. For the record, Randy offered to take them back and refund my money even though it was my mistake in using those LED's with Ultimarc's controller. I did purchase Ultimarc's LED's to replace them but I never got around to swapping them, so I still have those GGG LED's in my cab, which is fine because it only gets used twice a year, lol. Some day I will spend the time replacing all 24 LED's, if I am REALLY bored.
It is a good idea to be cautious when buying LED's to use with a controller that manages the current. Not all LEDs are created equal. The GGG specs on their website say that the RGB Drive II consume 20ma, so perhaps they use a slightly different LED component now, or maybe that is just a ballpark to calculate total current draw. Either way, the ones I got were slightly overdriven with the UIO and if I were doing it again, I would buy the Ultimarc LED's just to be safe.