I've used those high performance aftermarket starters and don't see any advantage to them. The stock GM gear reduction starter never fails unless it gets wet and rusts. I don't like the fact that the end of the aftermarket starters shafts are not supported by a bearing/bushing like the GM starter. What's up with that?
USCG approved doesn't mean that the Coast Guard tests starters to see if they are explosion proof. The Coast Guard doesn't have any testing facilities. A starter remanufacturer can send a starter to United Laboratories and have it UL certified to be explosion proof but very few do it because of the cost.
The decal installed on starters simply states that the starter meets the Society of Automotive Engineers (SAE) standards and when the Coast Guard boards your boat for inspection they may try and view the starter (if the starter is accessable) to find the SAE decal.
The new style GM gear reduction starter is the same for the automotive and the marine industry. When you are a marine mechanic you are constantly inspecting starters for water damage. I've compared gear reduction style automotive and marine starters on many occasions and there is no difference between them. I've also talked to many starter rebuilders and they also say there is no difference. There is a big difference between the older direct drive automotive and marine starters however.
Sincerely
Dennis Moore