Being that the T620 is a newer server you may run into some driver issues getting it to communicate with the MD1000. You are correct that it is considered unsupported and that is because this configuration was never tested. 
hi,  any supported or maybe only recommended Raidcontroller to connect an MD1000 Enclosure to an Dell PE T620 (Rackmount)? maybe: LSI MegaRAID SAS 928x Series with 2 external SFF-8088 Connectors for neighter Dell H800 or Dell H810 Controller ist listed as compatible with MD1000 (PERC external storage support matrix)  I think an PERC 5/E should work as well in an T620 (Rackmount) but would also be unsupported by Dell.  feedback is welcome.  kind regards.  Torsten 
PE T620 (Rackmount) vs. Dell MD1000