1) Whether you like it or not, Ventura was a SEAL: He graduated BUDS 58.
You can argue whether he was called UDT (Underwater Demolition Team) or SEAL on the basis that there were no SEALs when it was all UDT, but it's the same thing. UDT is still part of BUD/S (Basic Underwater Demolition/SEAL).
2) The lawsuit was against Chris Kyle and the allegations were against him. The involvement of his widow is only a necessary legal fiction because that's how the system works.
Chris was very much alive at the time he allegedly punched Ventura. A claim doesn't automatically vanish just because a defendant happens to expire. It was the court which ordered that Chris's widow be substituted as defendant. That's because she is the one who stands to benefit from Chris's estate - the entity that gets the profits from the alleged defamation.
So the lawsuit is not really against Chris Kyle's widow, or against his family, it's against his estate with his wife standing in his shoes for administrative reasons.
Not dropping the lawsuit is classless, but there's a lot of money involved and it's not Ventura's fault that Chris died.