Oh I did not know about 5V dummy load. What kind of load do you suggest to put on 5V?
Modern Power supply have most Power on 12 V and since we already connect GPU and risers maybe we don't need any dummy load?
Generally its not a good idea to run a PSU with no load, so if you are worried about that just attach a small fan to the 2nd PSU.
Just make sure that only one of your PSUs powers the motherboard meaning that the same PSU connects to the 24 pin power connector and the 8 pin CPU power connector, all should feed back to the same power supply.