My Wild Assed Guess would be that since Naltexone was designed to block the high, via pleasure receptors, when someone took opiates or alcohol for other than intended purposes... it shouldn't interfere with the pain blocking aspect of the opiate in question.
And, the dosage used in Low Dose Naltrexone are sooooo low... and of short duration, that it should be possible to take one without adversely affecting the other. but that is strictly my largely uneducated 'guess'.