While getting my tractor serviced by the Kubota mechanic he mentioned I could spray the hydraulic hoses where they all join up (it gets really dirty/cruddy there). I asked with what? And he said a pressure washer. I asked if that would damage anything and he said no. So that's my experience with it.
As far as type of pressure washer, like others have mentioned definitely gas-powered with a reliable motor like Honda. That's what I have and it's a reliable workhorse. I've never had luck with the electric ones. p.s. I bought my gas-powered washer off an online market site and paid half what it was new. Some ppl use them once to wash their house and then sell them, so it's a good idea to keep your eyes out for one. Of course if you do that make sure you see it running with no leaks. If it was well-maintained it should last you a long time