Will doctors perform Mohs surgery on an infected biopsy site on the lower leg?

Excellent question.  I would suggest you see the doctor who performed the biopsy.  They can clinically examine the area and take a swab for microbiology.  If clinically indicated, they can prescribe you a course of antibiotics and cleanse the area.  It is ideal for infection to be adequately treated before embarking on Mohs micrographic surgery.  I hope this helps.  I wish you well with your Mohs micrographic surgery.