As far as I know, dragon form does not give any bonus regeneration as a separate effect. However, regeneration is always based off of your current hp pool, and dragon form gives +50% hp, so your regeneration scales up with it.
As far as I know this page is still accurate despite being flagged as .15:
http://crawl.chaosforge.org/Regeneration_rateIf anyone spots anything that has changed on that page, let me know, and I'll update it and then bump the version number.
Edit: so far, removed a reference to chei long turns being capped at 10 auts, which they aren't anymore, and removed a line about trolls not benefiting from troll leather armor (they used to not, but now they do). Is it true that the amulets/mutation are both 40 regen rate? One of the examples at the bottom says 20, but the top part says 40, so I assume that 40 is the current value and the example is outdated. After that, should probably condense the vampire state information, as vampires have lost a few of the inbetween thirst states, and then it should be correct.