Yes, it's fine to suggest edits to a post's author via comments - the purpose of comments is to improve answers and this behavior falls within that purpose. The minimum character limit is mostly a crude measure to prevent certain abuses of the suggested edit system*, not a judgement on which edits are useful. Note that comments are often used to suggest edits for other reasons as well - for instance, if one wishes to make an edit that may conflict with the author's intent, it's better to suggest that to the author in comments rather than apply it directly. It is good practice to delete such comments once the relevant edit has been applied.
(*Also: this limit does not apply to users with reputation 2000+, who can edit freely)