No, not all FFA events require the uniform. Having just left three major shows, there were more kids dressed in nice shirts and jeans than there were those wearing the FFA full uniform. There were those that had on the full dress, and those that had on jeans with the jacket. The FFA uniform, (at least in our part of the world) is mostly used when they do the speaking contests, beef judging, stuff like that. Ours are required to wear them then, and to our end of the year awards ceremony. Our kids durin judgin have matching shirts that just have our school name on them and say Ag Mechanics.
And the girls can wear black dress slacks if they want to instead of a skirt.