You sure can. In fact, I did just that on the first bar I built. My pictures of Murray’s Pub are in the gallery. If I remember correctly, I used Helmsman, a similar product, and did two or three coats, and it looked great. That was on top of an oil based stain.
However, on my latest bar, Murray’s Pub 2, which I’m just finishing now, I used a water based stain, and then used a water based poly, and it looks like crap. So I’m sanding down the water based poly, and pouring Envirotex Lite over it. I did the beer gutter, and it looks much better.
But going back to your original question, oil based poly over a nice looking oil based stain is very hard, very durable, and very pleasing to the eyes. It may not look as thick as the Envirotex, but I’m sure you’ll be happy with the finished product.