Yes, base coat works as a top coat in a pinch… It dries hard and protects the color, and it’s usually not tacky. You won’t get that thick glassy look, since base coat is made thin and a bit matte so polish has something to grip (more on that here).
I’ve done this when I ran out. Looked fine, just a bit flat. The only time I got streaks was when I dragged the brush over polish that wasn’t dry yet.
If you want more shine, do one thin layer of base coat, let it dry, then buff with a cloth that has some cuticle oil on it.