If you want a top notch racer, you should actually just make the ski team just skate uphill back up the course and have no lift ticket at all, at least the slalom ones. gotta strengthen those quads.
I just couldn't resist... I started on a Nordic team and that's what we used to do when we needed to train on artificial snow... skate up for the training, then ski down and hope we didn't break our necks on our 200 cm + edgeless toothpicks.
Now, back to the OP's question. I think it depends on how the trainings are run. Usually there is a very short window of time that you have for training - and it's already outside of peak hours. The kids have to make the most of that time. Now if it's an all day training for an academy or something, you could make a case that the marginal cost of having the kids wait in the regular line is pretty low, especially during a 8-12 AM weekday block when nobody's on the hill anyway.
But when you show up to free ski on a peak day, you have a choice about which lifts to ride / which section of the hill to ski. Racers don't have that luxury. They are stuck. And if you don't think kids' time is precious, stop and think of all the other stuff they have to do in addition to skiing - homework, studying, practice instruments, scouts, "community service" graduation requirements, etc. Expecting a kid to show up at the mountain, for a two hour practice that consists of 5 runs and lots of waiting in line is ridiculous. True there is some waiting at the top of the course, but that gets worked out pretty quickly as some kids fall, others get pulled aside for 1-on-1 coaching, etc.
But, if you have a huge team of 20+ kids who all wait for each other at the bottom of the hill, hit the lift in a block, and make everybody wait, that's kinda bad etiquette. A small trickle of one or two skiers at a time cutting through the ski school like and jumping on with other riders as singles, it's not doing much to slow anybody down so you should just live with it and appreciate their dedication to training instead of being out causing trouble, or sitting around getting fat in front of the TV.
Also coaches (and racers who are with them) should without a doubt get to use the ski school line. The whole team waits for them, so time saved for them is multiplied for every skier on the team. And the associated headache of waiting for the entire group to be there so you can explain something at the start of the training. Coach can't pay attention to how the kids are skiing if they need to constantly explain what the drill is.
When I used to train at Sunday River for winter camp, we only used the ski school line for the first run of the day, and when we headed back from a break with the coaches. I think we got a discount rate, but honestly I don't know what the team had to pony up for to close off one of the slops. If you weren't a top five skier, you had to pay your own way, which I did several years and it was a lot less than what I would have paid retail. But it was definitely work, not fun.
My daughter currently skis at a hill where they offer a free development team. I have not seen a single racer playing "human slalom" or being disrespectful. However there are plenty of show off skiers who like to jump in the course - even when there is a racer in it - and cause falls or ruin focus.
And as far as lift line etiquette, I'll take a racer who gets up to the front of the ski school line and hops on with a single or double any day over a bunch of middle aged beginners who stand around yapping in front of the lift chute waiting for their buddies to make it down the hill.