I think you can, as their small print states:
Am I correct in thinking that if I've setup an account for the free 14 day trial, I can't use the starter packs on Greenmangaming or Steam to continue that character?
NOTE: The Starter Pack includes an activation code (“CD Key”) that can only be used to create new accounts or upgrade trial accounts; this game time cannot be applied to existing subscriptions. Using the Starter Pack to upgrade trial accounts created with the EVE Online Buddy Program makes the inviting player ineligible for a reward. To receive the in-game items included in the Starter Pack, create your character and click the “Redeem items!” button at the bottom of the character selection menu.
It seems to suggest to me that if you've set up a trial account, you can use a starter pack, but only if you've not used a buddy key. That's just how I read it though, best go with your own thoughts on the matter.
Oh for goodness sake, I've caught my scrotum in my zip again - Margaret Thatcher, 1986