Like all pasttimes ....the clay target games / have some rules and a certain amount of etiquette ....and you are wise to follow both....if you want to be welcome into a sqaud on a Trap, Skeet or Sporting Clays field ...
To the OP's original question ...is it dishonerable to shoot a Defensive or Field Gun - in Trap ....no. And it won't matter if you shoot it well or not ...
Shooting casually, at a local club is one thing .... you see all kinds of guns, guns that won't cycle, new shooters not really familiar with how to load their guns, poor fundamentals ....and as long as everyone is showing safe gun handling / having a good time ....few shooters, if anyone, cares. Most of us, as experienced shooters understand people have to learn / the squad might be a little slower / there might be some disruption ....its just part of shooting with "new shooters". Safety - is the only thing that matters !
In a Registered Trap Competition ...its different ...and most guys that want to shoot Trap seriously ...want to be on a squad with serious competitive shooters. They enjoy the rhythum of each shooter / the time they take between shots, the fact that their equipment is ready, they don't talk between shots, they stay rock steady when people beside them on the next station are shooting....etc ... To be on a "good experienced squad" is really important to how your shooting goes in a tournament. They will have their squads "pre-set" -- so they know the other 4 guys shooting with them. Even if they go to a registered shoot alone ....they want to squad with 4 other experienced shooters ...that they're comfortable with. But that's in a tournament situation - where one miss ....might be the end of your day.
Casual shooting at a club is different. Any new shooter --- that shows decent manners, respect for the rules of the game ....and respect for the other shooters on the squad ....will always be welcome on my squad / at least on casual days at the club. If we're just hanging out / practicing / having some fun ...we will always welcome a new shooter ...to the squad. Do I want spent shells bouncing off my gun, my back, my legs, etc ....No ....I don't. Nor do I want to shoot next to someone with an 18" barrel especially in a Trap Squad ....because I'm standing right next to the muzzle blast ....as they turn on an angled target....and that is way less than pleasant. So many clubs have minimum barrel lengths for Trap shooting ( like 26" ) ...so the other shooters are not disrupted. If a newbie is shooting a semi-auto and we only have 4 shooters total ...we'll leave the slot to his right empty ....so his flying hulls won't be an issue for anyone else. But like others said ---....ask if anyone minds if he's shooting a semi-auto / or use a rubber band to snag the spent hull.
If you're a newbie( or visiting any club for the first time ) ....show a little class ...be polite, talk to the squad leader before you go out to the field, introduce yourself, tell them you're new to all this, or that you have some experience, etc ... Tell them thanks / nice to meet them, nice shooting with them.. when you finish ....just common sense stuff....
If you do that - my hunch is you'll be welcome back to the squad again and again ....
Some of the rudest guys at my club ....are experienced shooters ...that are constantly running their mouths about how good they are, giving unsolicited advice to shooters, etc ...they may be good shooters / but I don't want they anywhere near my squad ....so none of this is how new you are, how well you shoot ....its how you behave !!