SAP HANA projects or applications may be divided broadly into four classes -
Suite on HANA - Here the the Business Suite (ECC, CRM etc) gets migrated from Suite on xDB (like Oracle, MSSQL, DB2 etc) to Suite on HANA. This is additional of a technical migration project however purposeful consultants play a serious role in testing and confirmative the configs post migration
BW on HANA - the same as higher than where bw on xDB gets migrated to bw on HANA. Functional consultants hardly play any role here excluding validation.
Analytics and Apps on HANA - numerous new Analytics applications (Enterprise HANA Models, Predictive Analytics etc) can be built on top of HANA. Here purposeful consultants play a serious role to supply all the business logic to technical team to create the apps.
New Apps on HANA - SAP is releasing a lot of recent apps on HANA where they're optimized and simplified to run on HANA. For example sFIN (Simple Finance) where SAP is coming with a new FI application having a single document for both GL and COPA.
Having said all the above, the functional consultants need not procure any specific knowledge to play their roles in assignments of 1/2/3 above. But basic understanding of SAP HANA extremely helps to a large extent.
My suggestion would for functional consultants to find out the fourth kind of applications that I have mentioned above.
Hope this helps