Building 2 projects at once from 1 install

Is building 2 projects (separate project folders) simultaneously with 1 unity install safe? Anybody tried this with(out) issues? I'm running unity headless as part of an automated build system.

I've got a game split into a client + server, so frequently I need to compile both. There's some stages of the build process that seem single thread limited which made me wonder if this is safe to do.