There is no way available currently that you can add the templates to a dreamweaver project and manage them there.
That being said, if there are chunks of HTML that are common to the various templates and you would like to manage that content globally, you could replace the chunk of content in the various templates that utilize it with a bit of code that includes the content from a TEXT (or html or htm or whatever) file in an globally accessible location. Like this:
In this way, you can simply manage the content of this (and the rest of your collection of text files) and all the templates leverage that content.
You might also be interested in this article: Castell Computers » Blog Archive » Conditionally Include Text Files in GoldMine E-Mail Templates
You could use a SQL Query to search through the HTML templates in the GoldMine SQL database and Globally replace text.
I have done this before, it is quite tricky but as long as you know what you are doing and have a good backup, it can work.
I know this is after the horse has bolted, but you should really think about managing the templates differently. Doug's article explains how you can control the content. You can also then manage the house styles and perhaps use signatures for marketing purposes. Use the User_var option to control user specific content. I would say that you have found the perfect reason not to allow multiple versions of the same template.
Using GoldMine email templates make it easy for us to manage global email content while still allowing some user control as Peter suggests. We use a combination of HTML and .TXT content as described in Doug's article to include a global marketing message in addition to unique signatures for each user.
We configure all of our GoldMine users to use the same default email template. That template includes a file reference to their unique signature as well as the global marketing content. The file reference consists of a common filename and path utilizing the Windows user's home directory in Active Directory Users <<file:U:\Email Signature.txt>>, but you could also use the local drive <<file:C:\Email Signature.txt>>. This allows the user to easily manage their signature file. It also allow the marketing team to quickly and easily update the marketing portion of the email template.