You can restrict a hover tool to certain glyphs by explicitly configuring HoverTool.renderers. There are several examples in the repo, here is one:
bokeh/hover.py at branch-2.4 · bokeh/bokeh · GitHub
The second question is not so clear. It is not possible to restrict the hover tool based on region or area (e.g. “only the left side of the plot”) if that is what you mean.