I've at least tried this with the primitive cells (like transistors) from xschem, you can generate the spice netlist, then in magic “File -> import spice” and that will drop in the cells. There's no intelligent placement, and depending on the spice file you're importing, you may not like the auto generated devices. I typically just custom create the analog cells I need, since I have to manually place and route anyways. I haven't tried the digital cells that way since I do those through verilog/open-lane anyways