There is training available for ministry workers, I see no reason why ministry-minded artists should not also be trained.
There does seem to be an inherent assumption in a lot of churches that if you can play an instrument, then you will do so at church. While many musos are happy to do so, I do feel that they are frequently taken for granted as just another congregation member helping out during the service, like the person doing the prayer, or the person doing the Bible reading (not that I devalue these jobs, as I do them myself and value them highly).
However playing an instrument, especially if you’re on your own, can require hours of rehearsal and be very nerve-wracking on the night. It can also strongly affect your enjoyment of the service. Furthermore, musos tend to be be heavily critical of their own work and seldom satisfied with the outcome - sometimes they aren’t given enough time to prepare, or the accoustics/audio is poor, or they themselves are simply not the best of musicians and are only doing the job because no-one else will. This is made worse by the fact that they tend to be the most oft-criticised member of the service, because it’s impossible to run a service where everyone likes all of the songs, and where all of the songs are played in everyone’s favourite style.
It can be a rotten job, and in some cases i think that there should be incentives in place.