I had zero freeze/zombie issues and a "set it and forget it" mentality with this config:

RasPi 2 (with freeze watchdog enabled)
MinerA (with auto reboot set when miner stops hashing)

One U3 would be solid hashing then die randomly;  and within 5 min it resets itself and bam.  back hashing.

I didn't rely on the solid red LED up front because sometimes when it went zombie or simply went to a zero hashrate;  the red LED was still lit solid....