The assumption that is being made with assessment is the ability of packages like curriculum, LORS and evaluation to provide an API where assessment will be able to deliver a user_id, an object_id (of the assessment) and a percentage value to, so they can process the result of the assessment for a user further into e.g. a final grade. Furthermore we expect the SS to modify the permission of a user on an assessment in a way that the user only get's "read" permission, once the mandatory (defined in SS) activities have been executed with satisfaction.
I hope this very straight forward technical explanation answers your question on the general interaction between assessment and the SS.
Now, internally the assessment system is flexible enough to enable a sequencing on it's own. This sequencing though has nothing to do with IMS simple sequencing. The assessment sequencing is used for branching, displaying multiple question on a page and then go to the next one. We do this on the one hand by checking items internally (is the answer in a valid range and how many percentag points is this answer worth) as well as externally (if the answer to question a is "b", then display question c and make an answer to question d mandatory.
If someone sees the need for an even tighter integration in the SS, then we would have to talk about the exact details.
