Is it possible that this could be referring to sharks in general, thus allowing the translation "Sharks are gray"?
Yes, it has both meanings: you could be speaking of a specific group of sharks or about sharks in general.
I'm not sure about the proper use of "gli". I thought it was for plural masculine before a vowel sound. In this case, "squali" does not start with a vowel sound.
Gli is used if the following noun begins with 's+consonant'.
yep, or "z"
L'orologio = gli orology
Lo studente = gli studenti s+consonant
Lo zio = gli zii before Z
You meant "gli orologi", right? Yes, L' also changes to Gli in the plural for masculine nouns.