Since inetd only starts the daemon when it is called its possible it doesn't show up depending on how you're scanning. Try doing a telnet to the port tftpd uses. This should make it start the daemon. (You can just do a for loop on the system like:
do ps -ef |grep tftpd
This will let you know if it starts the daemon. From your other messages it appears it is trying to however.
Looking for nobody in my /etc/inetd.conf I see:
talk dgram udp wait nobody.tty /usr/sbin/in.talkd in.talkd
ntalk dgram udp wait nobody.tty /usr/sbin/in.ntalkd in.ntalkd
finger stream tcp nowait nobody /usr/sbin/tcpd /usr/sbin/in.fingerd
Looking at nobody I see in /etc/passwd:
Looking in /etc/group there is no "nobody".
Looking in /etc/group for 65534 I see:
Doing a test from another system it worked fine so nobody itself is not an issue for me.
Your message complains about groups. You can change the entry in inetd.conf to specify user.group - The "nobody.tty" in my debian is specifying group tty which is in /etc/groups:
It might be worthwhile to specify a group