Interesting thread so far. Here are my $.02 so take it with a grain of salt and consult any legal professional for additional information.
I've done about 30+ wholesale deals in 2 years. We haven't had any issues until recently. I don't have a license and have gone by the process that you get a property under contract and assign your rights. We don't do double-closes (aka simultaneous closes). The contract(s) we use are fairly simple without much hassle (i.e., one page contracts) which allows us to assign our rights.
Given that, it all depends on the title company you use. We used a few that are familiar with our contracts and haven't run into any issues. We do have a few that were done through more big name title companies that have run into issues. As such, I have heard of some wholesalers being "investigated/sued". I'll be honest that I'm not too clear on the details yet but I believe it is from deals that went astray (not successfully and may have been ugly).
To sum it up on whether you need a license or not, it's up to you on your goals. If you want to wholesale, I say be wary of getting the license but also do your due diligence and know how all the pieces fit together. Wholesaling, although the cheapest point of entry for many new RE investors, is also, in my opinion, the hardest as you need to do many things well and consistently and persistently. I have wholesaled without a license and continue to see others do so as well. I believe it's more along the lines of if you are successfully completing transactions without issues, HAR/TAR won't bother you much. It's when things go awry that they get involved.