I have pretty much no experience with dihydrocodeine, but I'm going to answer what I can.
Apparently, DHC pills are pretty waxy and probably also hard to crush. For the most part, crushing pills will indeed increase the absorption of a drug into the bloodstream, thereby speeding up the onset of the effects.
Like hydro suggested you might be better off just giving them the ole chomp on the way down. That's probably what I would do, anyway.
While hydrocodone and DHC are quite different drugs, DHC is probably more similar to hydrocodone than codeine in some respects from what I understand. DHC isn't nearly as strong as hydrocodone of course, but DHC also doesn't have the 'ceiling dose' effect that codeine has. The names do sometimes get confused, though.