23% and 30 degrees has been around for a long time. It does not restrict you from flying in less light levels, but required you to have operational "pink light" installed on the acft. This was a requirement for Army training and operations which are tactical low altitude operations.
Civil HEMS does not perform tactial NVG covert operations. You probably have enroute minimum altitude of 500 feet AGL or higher and can only go below that after performing your high recon of the scene. Totally different environments. You also will have 2 or 3 unfiltered lights to help illumintate the area and if you feel you don't have good enough vision with the NVG, de-goggle and land unaided. NVG are a tool to make your job safer, enroute and at the scene, if you feel that unaided is safer, take the NVG off and proceed unaided. The really nice thing about NVG is you can flip them up and down as you wish and need. You are not limited to only aided or unaided. Get in the air and see which mode is safest for the conditions.
For your overwater oeprations at night, the NVG won't provide you much help unless oil rigs are not lit. I would recommend night overwater be primarily via instruments with altitude alerter set and resume NVG when approaching the shoreline.