Is wearing LEDs dangerous?
YES, there are potential dangers, and you'd have to take care of these in your design.

Assuming the LEDs are about 300mW each (30W total for 100)....then it's doubtful you could find any danger in the light output (unless close to the eye) or the power level (a 30W electric blanket). 

How you drive and connect the LEDs may indeed present some health hazards:


If you drive too many in a string, then the drive voltages can get into the 50-70V range, and this could become hazardous
You have to carry battery power for your application, so the size and protection you provide to the battery and it's wiring would be important.
Even at low voltages you need to ensure the wiring is protected.