Is the Wilson Supreme Cusion Design a basketball suitable for outdoor use?

Basketballs are usually made of one of three coatings:

• Leather: Intended for indoor use only.
• Synthetic/Hybrid leather: Can be used either indoor or outdoor.
• Rubber: Can be used either place, but more aimed at outdoor

(See this article toward the bottom for some explanation of these.)

Dick's also has a good explanation:

Leather may have a reputation for being tough, but a leather basketball should be handled with care. Basketballs made with leather are meant for indoor courts only. Surfaces like gravel and concrete can cause damage to your ball by tearing the material apart or flattening the raised surfaces which, over time, can destroy the grip of the ball. When transporting a leather ball outside, it may be tempting to dribble it, but this is one time you will find yourself in trouble if you don’t carry.

Basketballs made of rubber or synthetic materials are better suited for rough outdoor surfaces and will be at less risk for the same type of damage. Using the right type of ball for the court you’re playing on will go a long way in preserving the life of your ball.

Per the product description (and this was identical on several sites, so this likely came from Wilson directly, though they no longer list this ball on their own page), the Wilson Supreme was a Rubber coated ball:

• Revolutionary rubber cover combines high performance butyl rubber with sponge rubber for enhanced durability and a soft feel
• Indoor/outdoor use

As such, it seems like it is appropriate for outdoor use. You'll likely need to clean it carefully (use a toothbrush and soapy water) to help restore some of its grip, given its age.

While there's no rule for what makes a basketball an "indoor ball" vs. an "outdoor ball", indoor balls are typically made of full-grain leather while outdoor balls are made of rubber or composite leather.

It seems like the Wilson Supreme ball has a rubber sponge coating so I'd say it's designed to withstand outdoor use.

You mentioned that the ball is old; all balls deteriorate with use. Try shooting around and, if you find that the ball is slippery, you may want to invest in a new ball. Because rubber / composite leather are much cheaper materials, outdoor balls tend to be much more affordable than indoor balls.