Context is pretty important there. That is a situation during the week when they may do a more advanced dive at some more difficult sites. In that situation, you might need or want some help. On the other hand, it looks like you are a DM and would not need any hand holding. This is written for the many levels that show up on the boat. Contact them.
My understanding of the intent of the verbiage is to discourage people from coming to Guam and thinking that they can blindly jump into any waters.
If you are on a regular boat dive; organized shore dive or have free local guides (which you find by making friends with the shore dive group), you are not required to hire anyone. After the briefing and communication with your buddy, you will be quite safe.
Call or write MDA and ask for Dianne for travel info/coordination (Point out the phrase that gives you heartburn for a blunt discussion of the issue); Justin Mills for info on shore dives and Randy for equipment needs. I can put you into contact with several people via FaceBook if you just want a guide. They likely would do it for free for my asking or because it is Guam and such courtesies are expected. I took countless people in my truck to shore and boat dives. Several of us acted as instant buddies for new divers, people passing through or newly assigned there.
MDA's focus is the mainland US diver. They dominate that market for very good reason.
The mention of the shore dives is simple. You get a PhD educated (fish biology) guide, Justin Mills for FREE on weekends and there is a group of very advanced divers, most of whom are DMs with other advanced certifications who have hundreds of dives.
I envy you the opportunity to get in the water there - I would go in a second, but my tour ended and I am not likely to be reassigned there.