Something is attacking one of my trees...
There are several rows of evenly spaced holes in the ornamental weeping evergreen (species unknown) out front of my home. The holes are ~0.25" diameter, ~0.5 inches apart, and ~0.25" deep. Can I fill these holes with anything to ensure the tree stays alive (roofing tar?), and can I spray the tree bark with something to discourage further attacks?
This appears to be woodpecker damage.
See here for more information: https://extension.umd.edu/hgic/woodpeckers-and-sapsuckers
You say it is an evergreen, but we see little green. Does the tree have a lot of dead branches?
While sapsuckers will use healthy trees, if the tree is in decline or dying, it may have other insects within that woodpeckers are feeding on.
You should not treat the holes with anything. You willl see in the link above that you might try using wire mess protection to discourage them.
If the tree is important to you, you might check it's health with an ISA- certified arborist for an on-site evaluation.