
Lot of breeders use people who scan sheep as often they are more skilled at scanning than some vets so probably not just cost cutting why they did that opposed to going to vets - also, sick dogs go to vets so not ideal place for possibly pregnant dog... and if sheep scanner does better job with less money... I know where I would go with my girl!
I can't see any reason why you should walk away except perhaps that you do not seem to feel comfortable with the breeder.