xbtit has currently has support for SMF 1.1.12 or under (I need to look into why login is kicking up a fatal error in 1.1.13) but at the moment it only supports importing members from xbtit into SMF and not vice versa.
However there is a major upheaval to the password/cookie system coming to xbtit very soon which will make importing members from every known tracker source and also SMF/IPB forums a very easy thing to script around as we'll literally be able to copy the data from one users table to another because xbtit will support all of the password hashing types used in all these scripts by default.
This image is from my xbtitFM test site but this will be added to the regular version of xbtit almost* in it's entirety.
* The only thing to be kept out of the xbtit version will be the xbtitFM password hashing method.