Hi there Danny, and welcome to the FRA forum.
The build rules prohibit the use of hardened steel blades because of the danger that they can shatter under a hard impact.
Providing that the body of that blade isnt made from hardened steel and you dont run it in excess of the maximum speed stamped on the blade, then subject to the blade mounting hub, shaft and bearing assembly being strong enough to hold everything down I dont see a problem.
As with any spinning weapon the mountings are CRITICAL they must be strong enough to not only to support the blade but also be strong enough to withstand any impacts of other machines or your machine against the arena side wall while your blade is at full speed!
Remember, if your machine comes apart in the arena the only thing that gets hurt is your pride.. If it comes apart in your garage...!!! So please be very carefull when you are building and testing.
Good luck with your building and above all BE SAFE.. One word of advice... if you are not sure of anything..come here and ASK first!! we are always happy to give advice.