Just completed my first year of Griffith Dent, so can answer this one! (And will endeavour to answer other questions others might have pertaining to the course itself)
So yes, you can get up to 6 subjects (i.e. everything but the Dent specific subjects) credited for first year, and whilst a bit more niggly, there is provision to get 2-3 of the 2nd year subjects credited too (mainly Biochem, but Microbiol and Pathophysiology if you're lucky).
That said, whilst you absolutely can get these credited (and should) many do have to endure multiple application attempts before they are successful; Griffith will likely concede eventually, but you will be beholden to whatever fickle judge ultimately responds to your application. If you believe you are entitled to credit, apply and apply early, and continue to apply until they literally bar you from it - I have peers who applied 5 times before they finally succeeded. It's a pain, but ultimately worth it.
Personally my experience was painless, but your mileage will definitely vary