I think it depends on the company. If they have their own online forms, then you would need to fill that in, as submitting any other form than theirs would get disregarded and you wouldnt receive a reply.
If they just say “apply in writing” then yes, you could submit a generic catering application form along with a cover letter, it shows that you have researched and found a form to use, rather than just sending in a letter and your CV