A mix of both. The cattle keep his wooded acreage much more "open" due to grazing/browsing. Its pretty much impossible for the neighbors to access any stands without deer knowing...and where do they head? Right to my thicker woods where I don't pressure them.
10 acres of open pasture isn't going to support many black angus. He'll also find out how expensive it will be to supplement their food over the winter. My neighbor who runs cattle only does it from mid spring through September(ish), they aren't his cattle...somebody from the Dakotas hauls them here for the summer, then hauls them somewhere else for the winter.
Deer will adapt if he does turn it into cattle pasture, and you will have new, predictable deer patterns to hunt. I wouldn't worry about it too much ;)