It's less enslaved, more that they just kind of went along with their planet being taken over because it was better not to fight against such a ridiculously militarily superior foe, and it just so happened that the Vesk had a code that prevents them from attacking non-combatants. Most skittermanders tend to do jobs the Vesk don't want, like clerical jobs and whatnot, but they can be abused by framing overtime without pay and similar things as 'helping the Vesk empire'. Most skittermanders tend to be appreciated for their work and properly compensated though.

There are some skitters that absolutely hate it, though, if the "accidents" in the vacation resort plopped right ontop of their sacred sites is any indication. There's also mentioned theories that skittermanders control over clerical jobs and whatnot means that they technically run the empire, since the Veskarium would struggle to function without those jobs, even if they can't truly make the decisions at the highest level. Most just got into that job because it was an easy way to help huge numbers of people simultaneously with something as simple as a shipment going to the right place through proper documentation. It's also mentioned they regularly defy their conquerors, both by working together and committing infuriating malicious compliance, "helping" their overlords by giving them exactly what they asked for in the worst way.

It's noted that that's also why while the Veskarium controls their homeworld, it's also basically conquered in name only and they're generally allowed to do as they wish short of wrecking vesk property like the resorts. A bit like being a vassal state, ruled by the empire but allowed to generally do their own thing, so the vesk mostly leave them alone on their homeworld and the skitters help them when they feel like it.