We had some issues with not adding enough randomness in embedded devices, but that problem was largely fixed a year ago. At this point, I think urandom should be fine for session keys. It's not the best choice for long-lived keys in those embedded devices, but those devices (a) don't have RDRAND, since they tend to mips or ARM CPU's, and (b) since they don't have any peripherals other than the flash drive and the networking cards, there isn't that much entropy they can draw upon. There are things you can do to improve things in userspace, such as holding off on generating the host keys and generating the RSA keys for the certificates as long as possible, instead of right after the boot. But that's much more of a specialized problem for a specific class of system.