Research shows that Germans arriving in the Cape in 1780's were mostly mercenary soldiers from Europe employed by the VOC to protect the Cape.  A very good read on the subject is the book:  Cape Town Between East and West:  Social identities in a Dutch Colonial Town by Nigel Warden.  (Google the name and read from page 176 on Soldiers and Cape Town Society and from page 188 about the mercenary soldiers arriving.)  

According to him the following regiments arrived in Cape Town;  Pondicherry, Legion of the Prince of Luxenburg  (French) , The Swiss Meuron Regiment, Regiment von Waldener and the Wurttenberg Regiment.  According to records the Meuron Regiment arrived in Cape Town in February 1783 but according to other sources ( they arrived in 1782.  Which makes it a possibility that Hieronymus was part of the Meuron Regiment.  (Read more about the Meuron Regiment: and google the book 'The Swiss of the Cape of Good Hope, 1652 - 1971' by Adolphe Linda.  Read from page 169 about The Regiment Meuron at the Cape.)  The Regiment von Waldener and the Wurttenberg Regiment arrived from 1786.