Here are a couple of documents that might help in understanding the CS/HCM Split:
1297158.1 – Campus Solutions to HCM Integation: A Case Study on Integration Using the Owner Subscriber Option
1267773.1 – Campus Solutions CS – HCM Integration Support Released!
1259484.1 – CS Bundle #19 Functional Documentation for Campus Solutions 9.0 & Feature Pack 4
1320568.1 – Campus Solutions Announces Support and Documentation Availability for the Subscriber Only Model of the CS-HCM Separate Instance Integration