Except, on your 1DIV, (i) the flash synch speed will be one speed increment slower, (ii) high speed synch is not available, and (iii) "group flash" is not possible.
This info on 600EX-RT restrictions is from page 51 of the 600EX-RT manual. It's for EOS cameras released before 2012. Some older cameras (e.g. 1Ds, 1D, and many film bodies) cannot use the RT feature.
You can download the 600EX-RT and ST-E3-RT manuals from Canon USA. They're not on Canon Canada.
