Interesting Pete, I wonder if they did special code to support it. I know I can take my RS6 equipped Legacy T1 Duplex tender and try to use it with any newer locomotive with the RCMC and it doesn't function properly. That's specifically what I was asking Jon about when he described the changes in the RCMC operation over the R4LC for early Legacy.
While that combination may be customized to work, I wouldn't take it to the bank that you can use RS6 with the RCMC as a general rule.