I use LM15A to control several LED rope lights and they work well for that. As far as "is it safe" question. Since the LM15A as described on X10 web site, and in the instructions states it is for Incandescent lights, I think it would be foolish for anyone on the forum to say "yes" to the second question.
The problem is there is different types of LED bulbs. The bulbs with many LEDs (usually wired all in series) typically just use a resistor and diode to reduce 120V down to something that will not make the LEDs smoke. Essentially that is the way the LED rope lights function and are happy with my Socket Rockets.
Newer high output single LED bulbs using large die LEDs (Luxeon, Cree, etc) have some type of compact power supply buried down in the socket.
I have single die bulbs that have a tiny transformer squished in the socket which do work on the LM15A, however the LM15A will distort the AC waveform slightly and that minor distortion could cause "discomfort" with other types of power supplies.
About the only answer is for you to experiment with the bulb in a LM15A for a day and watch for heat or smoke....at least that my recommendation.