Does any one have a link for me to read up on security issues about hyperlink fields in data fields or perhaps just adding a hyperlink field?

Hyperlink that does what, exactly? It depends on what the hyperlink goes to.

It would be for members to list their site address.

Oh, I see.

There isn't really much of a security danger... as long as you verify it matches a URL regex expression and doesn't add malicious HTML code to be executed.