We used to get our NC house power washed once a year on the North side.
(and a few other shaded areas that used to grow algae/moss.)
The company used bleach, and it never seemed to bother the plants.
But we did water down the plants a lot to get the cleaning solution off the leaves,
and to water down whatever was seeping into the ground.
The plants did get some damage by the power washer...but not much.
I would be more concerned about any wood preservative getting on the plants.
I know when Bill used to put Thompsons Water Seal on our deck,
he would kill several perennials and annuals around the deck by getting it on them.