Absolutely. 420/422 reduce color resolution to allow 10 bit signal compared to RGB's 8 bit - witch is a worthwhile trade off in HDR mode. The difference between 422 and 420 is that 420 is quarter resolution color whereas 422 is only half res. Otherwise it's an identical signal.
Some TV's might allow a 12 bit signal in 420 but not 422, however that has no benefit whatsoever as virtually all HDR games will output 10 bit internally.
Best advice is to set automatic mode. It chooses the optimal mode for what you are doing. Other modes are just for older TV's.
Yeah, I have my PS4 and my Bravia all set to automatic. What I see happening is playing games at 4k with no HDR, it chooses 2160p RGB 60hz. When playing games with HDR, it chooses 2160p YUV420 60hz.
I presume this auto switching is ideal.
Also, for a lot of TV's you have to turn on a setting in order to get 4k HDR. On my Bravia it's called "enhanced HDMI"
If not, turning on HDR automatically drops the resolution down to 1080p.
Also, do not force HDR ON with your TV's settings. Leave it on auto. Otherwise the TV estimates HDR on software/content that isn't designed for it. Creates an overly harsh, ugly ass picture.