A link to http://www.wikitree.com/about/terms.html
could easily be incorporated into a Greeter's initial message. However, the recent moves to simplify the greeting and volunteer process would have to be reworked a bit. Changes were made several months ago so new potential members would not be overburdened (or scared away) with a lot of information in their initial greeting or confirmation. In addition, each new guest receives a welcoming from Wikitree explaining how to confirm their email, how to upload a gedcom, and provides links to how to use WikiTree, and introduces them to g2g. I think that no matter what we include in our greeting messages, there will always be that small percentage of people who will want to opt out for whatever reason.
Would it be feasible to include signing the Terms of Service at the same time as the Honor Code?