In all honesty I had never considered using CA in a wood to wood joint like that before reading that writeup. That being said, if Kevin Ryan says its good I wouldn't hesitate for a moment to follow suit. As with any joint I imagine that the precision of the surfaces is key to having a strong, invisible glue line. Keep in mind, Ryan uses a veneer on both the front and back of the headstock.
I would also hesitate to consider the typical "ear joint" a truly structural one, especially when veneering both sides. I cant really imagine a significant stress on the joint unless you have a tuner hole right through the glue line. Look at most headstock ears out there. After all the machining is completed there usually isn't a ton of material even left. No more structural than a heel cap IMO. That's assuming a "typical" headstock size I suppose. Certainly not the rule though, I'm sure you could devise a scenario which would ask a lot of said joint if you tried. Like anything else its definitely an operation worthy of care and precision.
Just my opinion....
Structural if you add tuners onto an ear or on the glue line.