Would wearing a hair system with glue attachment 2 months post SMP have any negative effect on SMP?

A regular tattoo is not the same as SMP. The SMP needles, with proper technique, are going in very shallow depth that is above the sweat glands. If this is the case, then no damage to the sebaceous glands.

Hair dye should be ok to use in 2-3 weeks. Please check with your doctor for any skin sensitivities and make sure the pigments used in your SMP treatment is high quality one. 

SMP into scar tissue can work very well. Pigment can take to scar tissue differently to virgin skin. It may take more sessions to build up a solid foundation for the pigment. Possibly the pigment will not be as stable. It is important to ind an experienced SMP technician in scar repairs.