if you bought them in the market then yes, everything you bought should show up in the market under downloads as purchased and you re-download them, as long as you dont start a new google account and use the one you were.
If you purchased them through the app store then the download history will be there and the themes should be on your SD card. Just transfer the SD card into your Droid 2 and you should be fine. That's what I did because the card in the original Droid is 16G and the one in the D2 is 8G. So gave my D1 to my roomie with the 8 G card and kept the 16g for myself. Like my D2 so far, not too many glitches.