Hello Sean B,
I dont think you can have single subnet associtaed with multiple EIGRP process, Consider EIGRP process 10 is running on all interfaces of Router R1 except one. It will builds up neighbhor with all connected devices running those process except one device connected to one interface which is running EIGRP process 20.
Redistrubution is the only option to make subnet availble between EIGRP process.
Redistribution in R1 to propogate routes learned from Eigrp process 20 to other neighbhors in Eigrp 10. After redistribution, other neighbors in EIGRP 100 need to ping the neighbor of R1 who is in eigrp process 20.
Redistribution of EIGRP Prcoess
Hope it Helps..
-GI
Rate if it Helps