Unlike other states that have addressed the issue, the Indiana bar has issued an ethics opinion (Ethics Op. No. 1 of 2012) which concludes that using "groupon" or other similar group coupon or daily deal arrangements to market legal services is probably unethical.
The opinion states that using these programs may violate a number of Indiana rules of professional conduct including rules 2.1, 1.15, 1.16, 5.4 and 7.2 because the programs would allow someone other than the attorney to hold client funds or create conflicts of interests or allow the sharing fees for referring clients.
The full text of the opinion is available here.
In contrast, ethics opinions in other states have found that is not unethical for lawyers to participate in group coupon programs. For example, see New York State Ethics Op. 897, North Carolina Ethics Op. 2011-10, and South Carolina Ethics Op. 11-05.