Using the same PayPal account for multiple sites is fine, but depending on how it's integrated on each site you may see the same "company name" on the PayPal checkout pages for both.
There are ways to solve this if it's an issue, but I would need more details about the setup of your sites.
That said, if you are running two separate businesses I would recommend that you do have two separate accounts for them. This will make it a lot easier on the bookkeeping for each.
If you happen to be using WooCommerce, you might be interested in our PayPal Multi-Account Manager plugin. It allows you to create rules that specify which PayPal account should be used for any particular order. This might help with whatever makes you want to use a single account and allow you to go ahead and separate them.
Hope that helps!
Angell EYE -
www.angelleye.comPayPal Partner and Certified Developer - Kudos are Greatly Appreciated!
