I personally do a fecal exam and have a IBD test done as well as a set of blood work. The blood work helps provide a base line for that animal for future reference. The fecals I run every year to 18 months for the complete collection anyway. There are a handful of serious transferrable disorders that I would not want to introduce to my collection.
I usually look for mites, RI, look through their feces for any parasites, etc. Have not done the blood work before, but each breeder/owner needs to do what makes them feel the most comfortable.