This is the same sort of thing as turning your gamma up so it looks completely bright - slightly modifying the games original options/files out of game, and is allowed, even though we have things like the Mining and Scuba helmet. The difference here is that invisibility texture packs directly benefit one group while making it a little harder for the others, and so people feel it's unfair. While everyone can turn their gamma up or hold down their mouse button, when selling drugs, only cops can benefit from invisibility packs, which is why no one complains about low fire or gamma.
I definitely agree that if these texture packs acted like tracers, and were very obvious, they shouldn't be allowed, however from what I'm seeing, the advantage seems pretty mild. The little dust-like thing that appears at one's feet in vanilla minecraft when people run with potion effects is much more obvious, at least in these videos, than the floating particles.
I think the problem lies more with the influx of cops, and those with super fast horses, as it's the start of the map, and the awkward ways of getting out of spawn. This map, getting out of spawn is harder, as there are a bunch of hedges, the jungle is farther from spawn than last map's park, you can fall in the water of the little water-lined shrubbery and be unable to get out. I wouldn't be opposed to putting barrier blocks above that damn water, or maybe a ladder! Maybe it's just me being horrible, but I fall in it all the time, even when not selling drugs. The tunnel is super camp-able and easy for cops to hide in, and the upper walkway is difficult to sprint up the whole way.
People can't complain in the same way about horses (though I will forever non-righteously complain about this, as cops should be jailed because they prevent us drug dealers from giving happy pills to the world) because druggies can get them too. This invisibility = tracers deal is something that automatically seems like a hack. If cops didn't have horses, anyone could easily outrun them and wouldn't care too much about tracers because on foot, drug sellers have Speed II and cops have nothing but the ability to camp doorways and corners.
I do find cops frustrating, and with this many, more stressful than fun to outrun, but I think there are other reasons for this, and other steps we can take, rather than disallowing a texture pack, to improve running drugs for everyone.