If you are doing it on a carpet track with no jumps then yes. There isnt a popular class for the 1/18 rally for racing Not sure what you would need to upgrade but i would so tires and some suspension work. Maybe a brushless system if you dont have one in yet. For carpet on road racing they do 1/10 and some do 1/12 scales. If you want to get into on road carpet xray has some on road cars. They are kits that you have to build. Some of those on road cars use the old belt drive system instead of the center driveshaft.
If you just want to race for fun with your rally go ahead but it wont do good competitively.