My suggestion to you would be to keep the usernames separate. I mean, I would suggest that you not duplicate names in either file.. use unique names for each. Just my personal preference.
However, although I don't know of any way already in existence to duplicate users in /etc/passwd and the .htpasswd files, you could easily write a script to automate this process, using the htpasswd -b batch processing switch, and useradd to facilitate the duplication.
In some cases, things that require specific attention, IMHO, are best left not being easy. One thing to consider is that a root user is needed to add new users to the system, whereas the owner of the apache server can just as easily add users to an htpasswd file.