FWIW, it appears from what you have written that your son is really at a crossroads in terms of what he wants to do and what he has to do to make a living.
As a grant writer, my focus is not web content design, but i do a fair amount of it as part of services offered to clients. The biggest issue I see for your son is gaining an understanding of how the programing is actually done. It's one thing to develop the words and text that will be presented to the user, it is quite another to understand the actual coding that is used to make the layout and design function when the user is "in" the website.
If the company has made it clear there is little room for advancement without this type of training, then your son needs to consider if he wants to make the investment in advancing his skillset to learn the programming languages for website design as well as Flash. If he does, my suggestion is to start with coursework either through Adobe Training
or a local community college. Specifically he'll want to have a basis in both HTML and XML as well as Flash.
Even if your son may be able to advance without the training, I think it would behoove him to seriously consider the training nonetheless. It would ensure he has additional skills that make him more marketable to other companies should the need for a change of jobs occur.