Sure you can.
Like I said, bubbles have error build into them already. Despite if someone knows it or not, there's already inconsistencies built into them as it is. I don't know anyone using a mercury level in the wild.
Also as I said, it's how you train. I was trying to articulate that if you don't shoot in different environments very often which is usually the case for most shooters then, yes, it will be hard to tell what is level. For the rest of us, we know how to look over the top of the scope, level the rifle, then fine tune the reticle level. I can probably count on one hand any top/respectable competitor that has a level mounted. Then ones that do, I have no idea if they actually look at it, or if it's a shortcut to looking over the scope.
Another splitting hairs convo. I'm all about levels, so I'm not trying to dissuade anyone from using them. Especially if one doesn't shoot a ton.