Ssh – getty start from command line

I have a line in my inittab like the following:

# Put a getty on the serial port
ttyS0::respawn:/sbin/getty -L ttyS0 115200 vt100 # GENERIC_SERIAL

If I try to perform a similar operation from an ssh session command line (this time towards a usb-serial adapter I have):

/sbin/getty -L ttyUSB0 115200 vt100

I receive the following response:

getty: setsid: Operation not permitted

Is i possible to launch the getty process from my ssh session and have a serial terminal be presented on the usb-serial adapter? Why does this have to occur in inittab?