I have 20+ different peoples kits at gedmatch, by 3 testing companies. Where the same person has tested with more than one company, only one is public, the others are marked "Research" so I can use to see minor differences in the company match lists.
To echo responses of others, Yes. Absolutely. The email address on Gedmatch simply correspond to the manager of the uploaded data, not necessarily the person who was tested. One person with the one email address can manage multiple data uploads.