Can I run a SRAM road rear derailleur with downtube shifters?
If you set the downtube shifter to friction mode then you can run any rear derailleur you want. If you're looking for indexed downtube shifting with a SRAM rear derailleur, the answer as of the date of this posting is no. Cable pull for SRAM is different than it is for Shimano and others, which is why mixing different brands of shifters and derailleurs is not advisable.