An interesting topic. To my knowledge, there are few marine electric dinghy hoists on the market that adequately lock the hoist cable with power off. The Rule 2200 (now discontinued) was one such hoist. Most dinghy hoists these days use simple winches, which have some degree of drag on the drum with power off, but do not lock. It appears most hoists advertised are really winches designed to PULL a load (such as a boat up onto a trailer, or an ATV out of a ditch) rather than LIFT a load.
In fact, there are a myriad of such winches, often available at other-than marine outlets (Cabellas, Off-Road Warehouse, etc.) that may, or may not work for your hoisting application. But be very careful. Few, if any of these winch manufacturers provide other-than winch "capacity" in there spec sheets. Nor are they designed as, nor advertised as, "hoists". Will they work? Sure, anything will work as a dinghy hoist. Until it doesn't.
For instance, what the heck does a "2000-lb. capacity" winch actually mean? Well, it typically means such a winch can pull a 2000-lb. load up some unspecified grade, against some unspecified coefficient of friction. It DOES NOT mean it will lift a 2000 lb. load. In fact, the lift capacity of that winch may be only tens of pounds, at full drum. And it's unlikely to lock that load mid-hoist, while you swing your dinghy overside.
There are true "hoists" available (Warn DC800, for instance) that specify a 500 lb line pull (ie-can actually LIFT 500 lbs.) at full drum, and mechanically lock that load with power off. Spendy (probably $1000 all-up, with synthetic line, and a remote power cable), but promises to do what I believe are essentials for hoisting safety, particularly on a boat. That being, of course, to lift your dinghy with an adequate margin of safety should your boat roll during your hoist, and lock said load mid-hoist to allow you to easily maneuver the dinghy onto and off the boat.
Sorry for the lengthy reply. It's not a simple topic, and (in my opinion) not adequately addressed by the marine industry. I've witnessed too many dinghy "incidents" caused by poor hoist designs to blindly run down to the local bait shop and buy the cheapest "dinghy winch" that purports to have adequate capacity for my needs. Personally, I'm going to spend the money for a hoist vs a winch on my boat. I value the safety of my crew, and the value of my property too much to skimp on an inadequate dinghy hoist.