I suspect there are different types of 510->901 adapters out there, some with KR8-compatible airflow, some not, so it's worth checking the specs/asking before you buy whether it will work with cartomizers.
901 batteries do not work directly with KR808 cartomizers.* The issue isn't thread compatibility (the threading on 901s and KR808s is, as I understand it, basically the same) -- the issue is airflow. KR808 cartos need more airflow through the battery end, and screwing them directly onto the 901 battery will make it impossible to drag on them.
There are modifications out there people have invented to adapt cartos to 901s, such as adding notches. Some people have tried drilling a tiny hole into a 901 manual battery charging extender. Some places (Nhaler is one I know) offer 901 to cartomizer adapters as well (which look just like manual 901 charging extenders but with a hole in the side).
The other way around -- KR808 batteries to 901 atomizers -- works fine with no airflow issue that way, I have heard (not verified myself). If true, this would mean that any adapters labeled as "510->KR808 cartomizer" should work with 901 atomizers as well.
*Some battery mods do have 901 connectors that are specifically made to work with KR808d-1 cartomizers. For example, the Super-T and PureSmoker mods' 901 tips accept cartomizers; I have heard the Chuck's 901 can do this if you request it of Jeff.