In 20 years of wiring machinery, I have never depended on a conduit to be a ground. Always run a separate wire for ground. Also, its always a good idea to bond it to both the machine and the end of the conduit connector.
Remember that conductor ratings are for "Free air"... 10 gauge is 30 amp wire.. There is some special "high temp" oven wire that is rated for more than 30 amps but I doubt you have any of that.
I suggest that 10ga is 30 amps.. derate from there.