If you have access to the plc programm there is a workaround. You can use the system functions DT_TOD and DT_DATE to convert a date into days and time of day. The DATE is an 16-bit value with the days since 1990-01-01 and TOD is a 32-bit value with the count of milliseconds since midnight. These value can easily be converted to a java date in Ignition.
I added a function to our plc programs that converts all DT values and stores them in a seperate datablock which is then read by Ignition.