I am not an expert of CIT-101 either, but I examined the schematic of VT100 keyboard for my project last year.
The VT100 keyboard port is a 1/4 inch stereo jack with these three lines:
Tip: +12V
Ring: Bidirectional serial line
Sleeve: GND
On the VT100 Basic Video board, the keyboard serial line (Ring) is connected to an LM393 and a 7416, via a complex RC network.
My suggestion is to check the traces from the keyboard port on the CIT-101 main board (it also looks like a stereo jack) against VT100 Basic Video board schematic. If you find an equivalent circuit, it is likely that VT100 keyboard is compatible with CIT-101 main board, or at least electrically safe to connect.
There may be other differences, say in UART clock speed or in the status bytes, but there is little chance that these differences cause hardware failure (please post a caution if I am wrong - I don't want to ruin anybody's unit).
By the way looking at several photos of CIT-101
here, l found that the CIT-101 keyboard has two additional keys, CLR/HOME and REPT, at the right end of the main keyboard. They are not included in the original VT100 keyboard. I am not sure if these keys are essential for operation of CIT-101.
Ryu