I don't know that inbreeding is an issue in veiled in the US maybe in the UK. If you look you can find reputable breeders like
@jannb that treat theirs like family.
I know one of the main problems for veiled is the conditions that the females and juveniles experience while at the wholesalers facilities. If you look way back on this site you can find descriptions of appalling treatment that many don't survive. If the females are not given adequate care then the eggs they lay will hatch out young that don't have the reserves necessary to grow properly. At some point in their development it will catch up to them. Husbandry, husbandry, husbandry. Once the stress of the pet store hits them they are already depleted, a week of that and the stress of a new home and we get to see it every day here, they are tapped out with one foot in the grave.
Jackson's chameleons from Hawaii are very inbred and it shows in their size and prevalence horn deformities. They also have another problem. Hawaii has volcanic soil and it doesn't release as much calcium as they would get in their native range. Their slower metabolism is probably the only thing in their favor because they are meant to live on less. The Kenyan imports are much larger thriftier animals.
I'm not advocating inbreeding but I'm sure we would see more problems with the Nosy Be and Nosy Faly's if it was too much of an issue. Between their island isolation and the line breeding for color they should be a mess. Yes, outcrossing is a superior breeding tactic and best practice but the occasional reintroduction of traits every
few generations can probably be tolerated as long as it is not excessive in chameleons (uncle niece not brother sister).
Ok now you can bite my head off.