If I'm reading your message correctly....Google is pestering you about creating a "Google" account to link to your business Gmail account?
But you already have a "Google" account, and it's tied to your separate, personal email?
That's just what Google does. They used to have separate accounts for Gmail, YouTube, Google,(The search engine), Google Checkout, Picasa, Google Calendar & all the other stuff under the "Google Umbrella". Once again, if I'm reading correctly, they only want you to make a Google account to tie in the Gmail address too. It's basically combining all of their services. (For example, you can "Log in" under Youtube, and when you go to Google search, or Picasa, or Gmail you're still logged in using the same account.
As far as I know, there's no way around this......since all their services are combined now. But, It shouldn't affect your work email. Just create & attach a Google account to your Gmail account & you're done. You'll continue using Gmail as you always have. The only difference being that you CAN (I.E., you don't have to) use that same account to sign into all the other Google stuff as well.
If you want to avoid having the business account tied to any internet activity, then simply log out when you're done using the business Gmail accountl. Nothing else will change. If you're unsure of which Google Account you're logged into, it usually shows in the top right part of your screen with a little drop down window you can use to log out.
I know it's probably not the answer you're looking for.....but there's no way around it since Google combined everything. On the bright side, nothing should really change since the only portion of the Google Account you'll be using is the Gmail section.