Actually, you can, but they won't have any of the new terrain types that Dom3 has (deep sea, caves, border mountains and the path specific site bonus terrains). For Dom2 maps, Arryn's site is the place to go.
There are going to be a few more maps shortly now that the Dom3 DB is mostly done. Give it time.
Also, the some old DomII maps are saved with alpha value, which Dom3 understands but DomII didn't. In other words, some maps are transparent and unplayable in Dom3. I understand at least one tga converter program has already beeen posted to these forums.