I suppose it's as possible to know this about composers with as much certainty as any other random fact, like if they had mis-matched color eyes or bad digestion problems! There wouldn't be any smoking guns in their musical compositions that would go "aha, impossible to compose without perfect pitch!" but it would be recorded in anecdotes in letters, that sort of thing, as it is for Mozart, as perfect pitch is kinda a party trick, especially in the era before Western music had a standardized pitch. Most musicians (and composers) of this and any era do not have it and do just fine with normal ole learned relative pitch. You may find this comment from yesterday by /u/erus about the history of pitch in Western music interesting.

For fun I've been racking my brain for any anecdotes about perfect pitch in castrati, and I think Gaetano Guadagni and Venanzio Rauzzini might have had it, as there is an anecdote about them doing a sort of party trick with pitch, where they went into a particularly acoustically receptive room and demonstrated Tartini's pitch experiments with their voices to amuse the court they were at. It's possible to do that without absolute pitch I suppose, but it would be damned hard! There's also the argument that perfect pitch can be learned, if you are exposed to music early, and both of those men would have been studying music since childhood, so if the claim holds any water, castrati would have all been well positioned to pick up perfect pitch more than other people. Of course Rauzzini was a composer and you've likely never heard his name before today, so I don't think perfect pitch, if he had it, gave him any unique compositional advantage!