I have ten gallons of used motor oil and never thought of using some of it to start the brush on fire.
It is a great way to get rid of waste oil and it burns very hot. Some will have a conscience about using it, but I think that a hot, clean burning fire is preferable to a smoldering failure of a fire. I have a neighbor across the road that likes to fill the area with smoke from wet leaves and brush and what smells like burning garbage. Hot fires don’t make much smoke.
Years ago, back when you could, we would burn brush piles at work. We were building a dam and fish ladder way out in the dingweeds on the Nisqually River. I was an extremely cold and snowy winter and the piles were hard to keep burning. My mechanic reversed the fan on the 966 front loader. We would back it up to the brush pile and use it like a massive leaf blower. Worked great!
I use waste oil with a bit of gas in it. Not a stupid amount of gas, just a bit to drop the flash point.