The company does not have to prove theft, unfortunately; being fired due to a violation of a company policy is itself grounds to be terminated "for cause," and someone terminated for cause is not entitled to unemployment compensation or insurance. Obviously, if you apply for unemployment insurance and the company does not contest or challenge it, that is one thing; in that case, you would collect. But if the company does challenge your application, they would have good grounds to contest it, and if they could prove that you were fired for violating policy, that would be grounds to deny unemployment.