I asked this of my lawyer a while back as I work with several growers/caregivers and we do sometimes share space. He said that it is fine but you do want some easy way to identify/prove who the plants belong to and that they are legal.

He recommended different colored pots or even tags with the patient/caregiver name on the plants, and for each grower/caregiver to keep a binder on-site with copies of their documentation proving they are legal.