I never saw a dive shop at the Radison (at least on the water).
most all the hotels there have some sort of dive "tour operator"
desk to sign you up for dives that all leave from some central
location.

Located on the property line between the Radisson and the
Aruba Grand is Unique Watersports.  Maybe that's who
they are referring to.
http://www.visitaruba.com/uniquesports/
They have a small shop and onsite boat at a pier at
that same location.   Their webpage says they are located
at the Aruba Grand, but they are actually on the side of
the hotel almost on the property line with the Radisson.

As for using them, I have heard good reviews about them.

Another boat operator, Pelican is about a 10 minute
walk down the boardwalk.   I was happy with them.

I only saw one dive site that was shallow.  that's
the Pedernalis, a WWII wreck in about 20 feet of water.
Some people like this dive and other hate it because
it is "beginner" shallow.  But I liked it because the
shallowness allowed good light for picture taking and
there were tons of fish eager to have their picture taken
because they thought you were from one of the snorkle
boats that give them fish food.

Most of the dives on the west coast are in about 50-60'.
The Antilla is the "big dive". It's a 400' freighter sunk
by it's german crew at the the start of WWII to keep it
out of the Dutch Marines hands.  it sits intact mostly
in about 55 feet of water and it's cargo holds are easily
pentratable.  

There are a few other wrecks and reefs in the 60-70 foot
depth on the west side.

the south side of the island has better reefs and deeper
ones (80-100' average)

on average, 2 tanks with tanks/weights boat dive was
about $55.  

hope that helps some.  drop an email if you have questions.