Not unusual, not against any rules and does not need the cooperation of prison officers. Thai inmates (and any foreigners) can also come to arrangements with other prisoners to work for them for a consideration and many Thai prisoners make it clear that they are available for menial tasks.
As can any inmate if they get parties outside the prison to have it delivered. It is not corruption nor does it need to inappropriately involve prison staff who receive the food and let the recipient know that it is there for collection.
Doesn't that depend on the kind of insurance policy they subscribed to?
Obviously, hence "perhaps".
In the highly unlikely event that there is no insurance cover, the local municipality will probably have a budget for that equipment.
Why is that relative to you or this thread?
It is not "relative" (whatever that means) to anything, I'm just curious about how much is at stake as you chose to go public with the subject which makes it relevant. Not my fault if it embarrasses you.
Does Immigration law state that using an agent is not permitted? It has never been an issue for many decades so why are you expecting "surprises" or are you just fear-mongering?