People have been ferreting for thousands of years, so of course you can ferret without them. I might get told off by some folk on here who INSIST that you use one, but it's simply not the case. Having used one though, they do save you a whole lot of hassle, less waiting, knowing where to dig etc, but if you feed your ferret up the night before you go, it may still kill in the hole, but it shouldn't be long before it comes back. About 25-30 mins at the most in my experience.
Having just stated that you can ferret without one, I'd totally recomend one though. Just ferret away and save your