Soldered RAM is fine for RAM disks.

Yes, absolutely. A RAM disk is a software feature, not a hardware trick. It doesn’t care whether your RAM is soldered or socketed — it just borrows a chunk of system memory and treats it like a fast disk.

You will lose everything in that virtual drive when the power goes out, and you are using up RAM that could be used for other things. But no hardware limitation stops you from doing it. Just set it up, and do not store anything there you cannot afford to lose.