Your separation agreement should be controlling as regards child support for college--does it stipulate who pays what for college--most SA's do.
If your husband transferred the benefits in order to reduce his income and thereby his spousal support or child support, his setting up the account in his name may be a fraudulent transfer, or it may be allowable so long as he disburses the appropriate funds to your son.
In either case, it would be well worth the money to sit down with a family law practitioner in DC (one who understands VA benefits would be helpful) and work through the details.
I would have your son contact the GI Bill / VA representative at the college and see what he can do to switch the payments to be made directly to him. This appears to be a fraudulent transfer as you husband is not attending college to obtain the benefit and is using your son's status to obtain this money (unless he is giving 100% of the money to your son which you make is sound as this is not happening).
Your son is an adult and needs to start standing on his own feet, so while you should support him, he should be taking point on this issue as it is his money. As the benefits were transferred to him and his father is misapproprating the funds, he could likely get his father into trouble with the military not to mention civil authorities.
I suggest you and you son approach you ex together and inform him he needs give the fund to your son or the matter will be pursued and that future payments are to be directly deposited into your son's account.
This answer is being provided as general advice only and is not to be relied upon for specific circumstances. By answering the question, no attorney-client relationship is created. As for any matter, it is best to seek consultation in person with an attorney who practices in the area of law in which you are inquiring.