I believe you can use OEM for everything except setting UserLED's.
I use DRO's and LED's in the 1800 range.
You can use SetOEMDRO(1800) and GetOEMDRO(1800).
And you can use GetOEMLED(1800), but SetOEMLED(1800) won't work, so you have to use SetUserLED(1800).
As for saving them, I don't know when the change occurred, but earlier 3.0 versions won't save DRO's in the 1800 range, but 3.42 versions will.
The Wiki says the User range was 1000-1254. I believe it's now 1000-2000? I know it was specified at some point on the Yahoo Group years ago, but i don't recall the exact number.