Currently the date format that is used in workflow emails is determined by the language of the user (user options) regardless of the Date, time, and number format chosen by the addressee.
If the user language preference is en-us, the workflow emails automatically use the en-us date format. As it is possible to work in D365 F&O in the language en-us but use the date format nl-BE, it should also be possible to receive workflow emails in English (en-us) but use the date format nl-be.