They will work together smashingly.
Battery life will be alright. I had the EMG-JVs along with an EMG preamp on my bass for 8 years. I only changed batteries twice a year, and even then it was only as a precautionary measure.
If you look at the specs on the EMG website and compare the EMG-JVs with their standard EMG-J, the JVs actually have a much lower current draw, and thusly a longer battery life.
I'm not sure how much of a battery draw the J-Retro is, but I can say that I know of several people who've praised the combination of active EMGs and the Retro. Yes, it'll all work off of one 9V battery.