i would like to know if lightweight mode APs (in a centralized WLAN then) are able to emulate a 3274 telnet session?
If you are asking if the LWAP system will pass Telnet 3270, yes it will.
If you are asking whether you can use Telnet 3270 to connect to the controller or AP for management or monitoring purposes, then I'm pretty sure the answer there is "NO."
If you are asking if the AP (lightweight or otherwise) can act as a controller (like a 3274) or agent for a controller such that it can manage TN3270 sessions to a host, I believe the answer to that is also "NO."
The wireless system (lightweight or otherwise) is just a substitute for real wire. Really nothing more, or less ... it's "virtual cable."
If a cable can do it (whatever "it" is), chances are good that wireless can do it too. The other minor services that wireless can provide (DHCP, for example) are only there in a limited capacity to support the wireless environment, usually for smaller installations.