I don't use AD enrollment but, updating your LDAP proxy and/or your AD servers (if they're not already) to use LDAPS is probably the easiest. Especially if you were already using AD authentication. Running it with a certificate and turning on SSL/TLS over port 636 is kind of the basis of that.
If you don't want to bother with that, you can still fully manage devices inside of Systems Manager. Configure your enrollment settings with a certificate authority cert, create automated enrollment profiles, assign profiles to computers or to users you create in Meraki, use tags to manage device and software deployments, and create profiles inside of Meraki and assign those to your tags.
Not sure what your current setup is but, there's a few ways get the end result depending on what you're wanting. Enabling LDAPS sounds like the cleanest option in your case since your basically there already without the encryption.