Hi Tim ,
Missed your post but there is : OFFT wich meets in Utrecht ones a month during the winter. Next meeting is 13 November see the website : http://www.offt.nl/ i dont know if the link is clickable but the adres is correct.
There is a admission fee to overcome the cost of renting the place of €4,-
Then there is Aquashot : http://www.aquashot.nl/ wich is founded by the NOB to stimulate the growth of the underwaterphotography ( and video ) in the Netherlands there are subdivisions ( regios) in wich people come together and evaluate and give positive criticism . Probably zuid-holland would be the one closest to you.Don't know if these are very active , i'm in Noord-brabant and we have a meeting end of next month
Hope this is of help and feel free to write a pm if you need some help with the dutch websites