words As I have said, I don't have GrapheneOS or a Pixel phone yet. I'm hoping somebody who shares the use case of myself and OP can confirm whether or not it's working.
I've seen posts suggesting it has worked before, to then be broken by a later update. I've also seen threads suggesting it was broken and was then fixed after an update. The current state is therefore not clear.
As for ADB: I'm not in a position where I require the highest security. My habits avoid situations where security is an issue out of my own hands. I wouldn't consider ADB to be a risk as I'm familiar with it and use it often.
To this point by secrec I don't want my phone controlled entirely by the recommendations of the GrapheneOS developers. People have different threat models and therefore can afford to take what would be a risk for some users.