It also sounds like the light's dimmers (not the lm465) may have a switching power supply in them, and SMPS's don't normally like to be fed phase angle AC (triac dimmer that the lm465 is).
The night light is a purely resistive load and maintains the phase angle control from the lm465 allowing the triac to trigger, where the SMPS is a non linear load. The input to SMPS's are normally a half or full wave bridge rectifier, and do affect a triac's triggering angle.
I have been using this type of lighting on a track light, with one of the lights a 25watt incandescent for just the reason that you have done with the night light.
I have not had any problems dimming these lights, but each SMPS is designed a little different so not all will work.
Use your night light along with the high intensity lights that you have and give it a try.
Monitor the lm465's temp (by feeling it) and if it gets hot, try something else.
You may damage the triac (usually goes open), but I would guess that the nightlight should keep that from happening.... YMMV and I cannot guarantee that it will work for you.