I have hundreds of altcoin rigs running 2-3 PSUs.....there is no reason not to especially since you can power the graphics cards off of higher end server power supplies at a fraction of the cost of an expensive ATX supply.
You can buy a cheap no name brand ATX psu to power the board and run a high quality PSU on the graphics cards.
The price of dual PSU is much cheaper than single PSU
Enermax 1500 watt is $250
Enermax 700 watt is around $70
Atx connector is only $7
So dual PSU is far more cost efficient.
However, some says we need higher quality PSU. I have no idea why.