Question
Can lawn fungus affect other plants?

Answer
The short answer is "Yes!"
But... the lawn is a continuous host. A fungus has no problem here. The spores (like eggs) are always present. When the conditions (usually temperature and moisture) are right, these spores hatch and spread rapidly over the whole lawn.
If there is a shrub in the way, it will be infected also. But the spores might have settled on the outside leaves only; or the inner areas of the canopy might be protected from the temperature change. These factors will limit the severity of the infection on the particular shrub and prevent spread to other shrubs if they are not close by.
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