Can a grey seal swim in the same water as the subject of Moby Dick?
The range of gray seals is limited to parts of the northern hemisphere bordered by the Atlantic ocean. The subject of Moby Dick was a sperm whale. Sperm whales can be found in the north Atlantic, in addition to most other bodies of water on earth.
The answer is yes.

Would a slingshot be improperly classified as artillery?
Artillery refers to ranged weaponry that is predominantly used in breaching fortifications. Examples of artillery include: howitzers, mortars, and rockets. Mortars can have a range up to 4,680m. A slingshot is a string weapon that propels a rock or other small projectile. Some slingshots can fire projectiles up to 9m.
The answer is yes.

Is Christmas celebrated during winter?
Winter begins around December 20. Christmas is celebrated on December 25, a few days later.
The answer is yes.

Did brother of Goofy creator's employer commit an excommunicable offense?

Goofy was created by Art Babbitt who worked for Walt Disney. Walt Disney's brother, Roy Disney, was a member of the Freemasons. The Catholic Church has a litany of offenses that can get someone excommunicated. Being initiated to Freemasonry, is listed as an excommunicable offense.
The answer is yes.