Update (for any with similar question):
Success with BlueZ in 3.14.52 Kernel / BlueZ 5.39 (made w/Builroot 2016.05 release): `gatttool` reading of peripheral characteristics; `bleno` acts as peripheral without any found problems.
Fails (in spectacular manner) in 4.1.15 Kernel: `hcitool lescan` returns devices. `hcitool lecc <mac>` hangs, then WiFi dies. No amount of reinitializing, unloading-reloading kernel modules, etc. fixes.