It depends on what you're doing. No you do not need a lawyer to buy a short sale or sell a short sale. NH does have a law called 479:B in which only certain individuals ARE EXEMPT from submitting particular paperwork to a homeowner when they negotiate a short sale. One of the exempt individuals is a lawyer. It can be a real estate agent, mortgage broker, etc. I encourage you to look up the law to see who is exempt. If you are not one of the exempt professions, then you need additional papework added to your short sale negotiation paperwork.
You do not need a lawyer, bottom line, but it certainly doesn't hurt depending on what you're doing.