I'd just cut it back away from the base of the rhodies. It is a common planting combo here but vinca has the potential for growing up into or overwhelming small shrubs and perennials, so some control over its spread and aggressiveness is warranted. You may find this will need to be at least an annual maintenance project :-)

If your question about fertilization indicates the shrubs appear to be struggling or lacking vigor two common problems with these are honey fungus and root rot. In both cases the root system is being attacked resulting in stunting and decline of the top (also there are water molds related to those that cause root rot that attack the branches of rhododendrons directly).

In the case of root rot this is often fostered by the planting site soil being too heavy and poorly drained to really suit rhododendrons fully. This is a common circumstance in my region of glaciated soils where even the native coast rhododendron only occurs naturally here and there, is absent from large parts of what is otherwise its wild range.

i used to cut the vinca carpet with pruners.. or scissors .. and create a nice mulch circle under other things ... i would also gently prod out any rooted in parts.. and move them elsewhere if needed ...

i never fertilized anything due to vinca sucking up all the good stuff .. crikey .... the stuff can overgrow cement happily ... how much of anything can it need .. lol ..