Can I assume that nobody is 65534?

You can't. nobody has had at least a few different IDs across distros and time:

Historically, the user “nobody” was assigned UID -2 by several operating systems, although other values such as 2^(15)−1 = 32,767 are also in use, such as by OpenBSD. For compatibility between 16-bit and 32-bit UIDs, many Linux distributions now set it to be 2^(16)−2 = 65,534; the Linux kernel defaults to returning this value when a 32-bit UID does not fit into the return value of the 16-bit system calls. An alternative convention assigns the last UID of the range statically allocated for system use (0-99) to nobody: 99.