Can I run aluminum backed organic brake pads with Elixir Avid 5 hydraulic system? The old pads were steel.  I bought the aluminum thinking they would disperse heat better but if it's going to cause a problem with the braking system I'll go back to steel at less than half the price.
Yes, there are aluminum backed organic brake pads available for the Elixir series brakes.

The SRAM part number is 11.5015.040.020 with the description [Disc Brake Pads Organic/Aluminum - Elixir 20 sets], according to the 2014 SRAM Spare Parts Catalog.