The only non-Starter, non-Legendary Pokemon you couldn't get in Diamond and Pearl were Tropius and Tangela, oddly enough.
But there were various Pokemon who would only appear if you had a GBA game in the DS' slot, so technically they can't be gotten through DP alone...
They're finding freaking Nuzleaf and Shiftry prior to Oreburgh City. You could only catch them in Route 229 with RSE inserted in the GBA slot.
I've said it before and I'll say it again. Dawn is the freaking best.
Edit: I don't understand how one can "dodge" lightning.