Yes, vet the horse. Just because it has a 2 year warranty, it doesn't mean you will always have a come-back. How, for eg, would you prove, with the absence of any vet report, that the horse had whatever problem when you bought it?
Definitely vet, I made the mistake of not vetting a purchase once, the horse became unrideable after 6 months and had to be retired. A warranty doesn't always mean anything.