The TFTP (Trivial File Transfer Protocol) is part of the standard Internet protocols. A/UX B-Net (Berkeley Network) supports most Internet protocols like TCP, IP, FTP, TFTP, SMTP, ICMP, UDP, and so on.
Yes, the TFTP client and server model have been supported since the first release of A/UX (1.0). /usr/bin/tftp and /usr/etc/in.tftpd in A/UX are the TFTP client and server, respectively.