My faction does this a lot. Flying, ipecac or wrong blood bags, Small Explosive Devices, attacking offlines with stricken, mercs, all of it is fair. We have even had stronger allies assist us using a strategy we call holding. They attack whoever is watching, but don't click leave, mug, or hospitalize, because the fight isn't "over" they cannot med out until the fight ends itself in 30 seconds, giving us time to hit whoever we need to, whether it be to turtle our own or score points. I have had people complain about it, only to start doing it themselves because they couldn't hit us, but we were fast enough to jump out, hit, and turtle again, so they had to turtle too.
If you want to see one that is "disrespectful", but still very legal, check out [This Post] that was written by one of my members about a strategy we used. They needed about 9 more respect to earn caches, and the last few hours of war, we used SEDs to put all of us in the hospital and quit playing the game for a few hours while the clock ran down. Needless to say, they did not get caches.
I find that if your opponent is complaining, you are on the right track. They complain because it is hard or time consuming. Good. Make them earn their rewards, if they don't have time to war, maybe they should reconsider enlisting.