I have made QNX 6.1 host as a server and have created /etc/issue and /etc/gettytab files with proper formatting. But, when I telnet to the server, the message doesn’t gets printed before login prompt.
Is this supported in QNX 6.1? If so, how can I get it to work?
I don’t think so. Our /bin/login doesn’t use those files.
I read that it was supported in QNX 4.x. Whether QNX has removed this in the later version (6.1, 6.2.x)?
If I compile the GNU source code for login, telnetd and inetd, can I make it to work?
It might yes. And you might also break your system. 
If you do try this, learn about pkgctl to restore the original binaries. I doubt you need to touch telnetd or inetd btw, just login.