I have co-cultured human macrophages with mouse and rat vascular smooth muscle cells in the past. First consideration would be your time frame. If the Schwann cells are proliferating and you would like to make co-cultures, like i did, for 14 d you might think about stopping the proliferation. I have used MitomycinC. Than you should also think about a label (like celltracker) or stable GFP expression (i.e. using a GFP knock in mice). I have used a xenogen co-culture formulation to make use of species specific real time PCR to measure the expression in each cell type seperatly.
I hope that will help you, feel free to specify your questions blow.