I would only use my licensed electrician and plumber. As a licensed home improvement contractor, we are only licensed to perform carpentry and remodel work not the mechanical end of it. Some guys do all the work but are not licensed to.
A licensed and qualified electrician and plumber. My license only permits me to perform the carpentry and finish work not mechanical work. Some contractors do all the work and are not supposed to.
Typically the General Contractor hired by the Homeowner hires subcontractors to install electrical and plumbing fixtures in a kitchen project, although on a small project they may have their own workers install them. In either case a licensed plumber and licensed electrician must oversee and be responsible for certain tasks, such as adding circuit breakers or roughing in new plumbing fixtures, although non-licensed personnel may do the actual installation.
If a homeowner is going to provide some lighting fixtures and/or buy their own faucets or sinks, the contract should spell out in writing who is responsible for installing them.