[inactive archer squad]
They went back to being civilians and performed their civilian duties. How will they use an archery range that their squad is set to actively train in if they're set to inactive on training?
That's easy then, you gave them civilian duties. 'Inactive' archery practice is a spare time job and will be done primarily when no job is available or when the dwarf is on break. To give them more opportunities, free them from hauling labours and optionally delete other jobs from their list.
Seriously, i've seen many complaints about dwarfs not practicing archery while active, and yours is the only statement i can recall that claimed inactive archers wouldn't practice. With enough spare time, off-duty archers will practice and improve their skills very reliably; quite a bit more slowly than sparring melee soldiers, but about twice or thrice as quickly as off-duty, 'individual combat drill' only melee militia.
Newsflash!
Active training of archers totally works!
I checked what had been suggested by some on these fora and the results are impressive.
The setup was quite simple - volcano in a 'minerals everywhere' world, invaders off since this was just testing anyway. In spring i set up a pair of archery targets and waited for the first migration wave. As soon as the wave arrived, i drafted two of its members and made them an active/training two-dwarf archery squad. One was a ranger with novice marksdwarf skill, the other a peasant who'd just turned twelve. Expectedly, they instantly started loitering around with the job 'going to archery practice', without actually moving to their assigned targets.
_Then_ i installed the armour stand and defined a barracks encompassing the archery ranges and set the squad to train there.
That was what was needed - they instantly went to the barracks and started training. First a bunch of demonstrations (the ranger had not only marksdwarf skill, but was also a novice in dodging), but once they were happy with their respective skills, they started shooting at the targets non-stop. They occasionally idled for a few ticks after picking up new ammo and needed to take a 'go to training' job to return to the barracks/range, where they also needed a quick 'organise session' job before returning to practice, but the amount of wasted time was negligible. I let it run until just after the year change, and in those ~seven months of training the two of them had gone from novice/no skill to adept/talented.
I suspect that this success was helped by the almost complete lack of interfering skills - the only non-archery skill present was dodging, so they spent little time on demonstrations. I don't know whether a larger squad would have run into the ubiquitous training interruption troubles, but i think the bigger problem would be the immense ammo consumption.
My assessment as of now is:
active squad - to train up a few high-level marksdwarfs fast, better look in on them from time to time to make sure they're practicing properly; they need the comforts of active military to stave off unhappiness while levelling up.
inactive squad - somewhat slow, but very reliable and practically maintenance-free training of sizable archer reserves. No happiness management required because they practice in their spare time, as civilians.
To reiterate: active archery squads _will_ use archery targets if those targets are inside their training barracks.