No, the V.24 connections need to use a null/crossover cable. See here: http://www.qsl.net/kb9mwr/projects/dv/a ... facing.pdf
The easiest way I've found to do it is to make a short cable terminating in a keystone jack and punch the crossover connections there, then you can use any Cat5 cable between the keystone jack and the second Quantar. V.24 null/crossover is required for a direct connection between a Quantar and any other device, be it a DIU, AstroTAC, or another Quantar.
Yes, RT/RT needs to be enabled in the Astro Wireline config. RT/RT is only used when connecting two Quantars back to back (side note: P25NX "tricks" the connected Quantars into thinking they're only connected to one other repeater, which is why you need to enable it for that.) You also need to set the External Transmit Clock to Disabled.