As long as the stipulations in the grant approval / contract allow it, services financed by funds designated for work contracts (third party services) can be performed by others. Here one must take into account that the subject of a work contract can only be one specific performance, for example, submitting a report. Describing mere activities can not be the subject of work contracts. Note that these do not deal with personnel expenditures but rather with material expenditures. If a project is processed primarily as a work contract, it no longer can be regarded as a research activity of the university but rather as tax liable project management.
Work contracts are also reviewed by the administration and then signed by the president or rather by Department B on his behalf.
For questions about pseudo-self-employment, tax liability, and compulsory insurance, please observe the section about External Services.