I'm not sure that a crabapple needs to be triploid to be
effectively sterile. I have a crabapple that I wasn't sure
was initially an apple. It has quite serrated leaves, often
tri-lobed. It flowers after my one crab is completely done.
It has solid, I'd say almost shell pink or salmon pink flowers
(and buds). The flowers are double or semi-double (and
doubling is often at the expense of anthers). It does set
some large, almost apple size fruit. They might be useful for
cider, but are inedible otherwise (tannic/bitter?). I don't
think that in general this tree, although attractive and a
good bloom time for ornamental purposes (after most other
flowering trees are done), would be a good pollinator. The
picture of Prince Georges (although hard to see) reminds me of
my crab.
Also this link http://www.agric.nsw.gov.au/reader/7215
indicates that honey bees may bypass differently colored
flowers (note that this site is Austrailian and they have only
honey bees and no bumbles.)