There doesn't have to be air in the pump basket for a suction side air leak, though there almost always is. An air leak in the impeller housing would not visibly show any air in the strainer basket, but then pumps hardly ever leak there.
The does have to be air in the filter if you have a suction side air leak.
The spa jets can still draw a little air even if the blower is off. Some kinds of jets draw a lot of air with the blower off, but all jets that work with a blower can still draw at least a little air even with the blower off.