Very likely. I do not know how the design should be but ideally trucks should have easy access to many docking locations. Perhaps you cannot do it for all slips (such as internal slips) but in that case you have adequate locations where boats can load and unload tanks. Whether that is viable is something that needed to be worked with the dive shop owners before a design is even put on paper.
Time will tell.
Is the marina purposefully built only to service dive boats? If it was then I'd agree with you that if you're building a marina to serve only a niche then it would be smart to build it to serve that niche.
If this is just a generic marina, which will serve dive boats, catamarans, fishing boats, pleasure boats, sail boats.... then you build it like a typical marina and loading and unloading tanks from trucks to dive boats wouldn't effect the design. I've never seen the place so I don't know what it was built for, but if it's built for all types of boats the owners needed to design it generic enough that different types of boats can use different slips, that way you can rent out all of the docks instead of having some empty because they are purposefully built for a specific use and there are no takers.