Yes, you can manage all your domains externally if you prefer.
Most domain name providers supply you with a control panel to manage, amongst other things, where your domain names point.
A domain name provider will let you specify the server to which your email is sent (MX records) and the server on which your web site lives (A records). These can be entirely different servers.
These settings are the equivalent of saying:
- I want the email for hostingreborn.com to be handled by server 78.31.104.54
- I want www.hostingreborn.com to get my website from server 78.31.104.56
You can by all means use your domain name provider's control panel to point your A and MX records to one of your hosting accounts.
Open up the given hosting account's management screen to find the server IP address you need and follow your domain name provider's instructions.