Is it likely no, does it happen yes. Do any of those two statements mean anything if its your mare in foal to a stallion you don't want her in foal to? As with all things practice makes perfect and why let this little guy "practice" if he will never be called to serve. I would say geld him and if he has not dropped in six months (assuming he is a yearling) than assume he is a crypt and take the appropriate steps. Gelding will really depend on the vet and the size of the horse.
In most cases, mini's cost less in after surgery antibiotics; however, the tranquilization, procedure and risk to the doctor are all remarkably the same. People might think its safer because its a small horse but the doctor is performing the procedure on their knees (if they do standing procedures) so the risk is remarkably similar.