yes, they are valid if done by the owner BUT if you ever sell a goat and say it is tested later as positive then they could come back on you and say you must have drawn blood from a different goat, labeled it for that goat just to get the negative results. If done by a vet most people will think that the vet made sure it was the right goat the blood was pulled from. Almost every person I know, including myself, just draws the blood themselves and sends it in. When you have a bunch of goats it can get pretty pricey to pay the vet to draw the blood, come to the farm, examine your animals, etc.
Technically TB and Brucellosis testing must be done by a vet to be official and to be counted by the state as the whole herd (or individual) being tested (if you are wanting to test yearly to be a certified/accredited herd) but that is mostly because both diseases are very serious (not that CAE isn't) and can be spread to other animals including wildlife and people.
Vet sent our test to Perdue University (Indiana) for testing. Results we got were Negative for CAE antibodies. Wondering how sure this test is. One of those tested was inadvertently fed frozen milk form CAE positive doe for a couple of weeks after she was 6 weeks old. Was thrilled with the Negative result but want to be sure.
If the test was an ELISA test it should be pretty accurate. AGID is the other type of test some labs run and it isn't very reliable. I would retest the doe you know was fed + milk in a few months but use either WADDL or BioTracking as both labs are pretty reliable.
If the owner of the goats draws the blood themselves and sends it in for testing, yes, they can get test results from that and use it as "proof" of their herd testing negative. I suppose going through a vet for testing would be ideal, though it's obviously going to be more expensive. But doing so, maybe there would be a less likely chance of mixing up blood samples and the owner couldn't "cheat" when having blood drawn. An unethical breeder, I guess they could just draw blood from a few of their already negative goats and claim those blood samples belong to different goats. I don't think that goes on very often, but I'm sure there are people out there like that in the goat world who would try it.
I'm wondering if your vet isn't talking about for health certificates or something. Then I can see where an owner's test results that they did on their own wouldn't be "valid" for a health certificate or something.