I have fixed the $TERMVT100 driver ( PORT TYPE 8 ). So the VT100 and VT320 telnet sessions should work a lot better.
You will have to re-download the D31 IRIS to get the new driver.
None of the free ones I have tested can do blinking characters. But TeraTerm Pro does provide an alternate color to represent blinking.
Daves Telnet does not appear to be able to do the Dim mode.