You seem to assume that SAP HANA performs operations on the actual values of columns in a table.
That's not the case.
Instead, most of the very base operations like filter, join, project are performed with so called value-vectors. Only when the data needs to be materialized, e.g. to create a human readable output, the actual values are pulled from the so called dictionaries put in place.
The openHPI and openSAP courses about in memory databases cover that quite nicely.
So, to answer your question: don't bother "optimizing" your table design by making funky data type choices.
If you need a surrogate key, then create one.
If you don't need it,don't.
You can save storage by picking e.g. a numeric data type for numbers instead of a character data type - which is important in itself. But this won't have a tremendous impact on the join performance.