Angled holes might not be the end of the world, but I wouldn't trust them. If you're using wood screws, there's some forgiveness because they'll screw a snake if you'll hold its tail. They'll go anywhere without concern, is what I'm saying. They just dig in. Take apart many Fender necks, and you'll be surprised at how sloppy they are. Might even see extra holes for no apparent reason, but I suspect it's because they're just driving those screws in with a 3/4 HP driver and calling it good. If not, try again. Never mind if it is good - theoretically, nobody's ever going to see it.
My concern would be that they'll pull funny. I know when I do threaded inserts in neck heels, I go to a great deal of trouble to make sure they're exactly perpendicular to the neck and body, both. Otherwise, they'll cross-thread and you're stuck inventing a new batch of cuss words to go along with the ones you already know to express your anger and consternation.
If I used wood screws to hold the neck on, I'd want those to pull perpendicular as well. You want the neck joint to be tight as possible and angular fasteners just aren't going to get you there. Same as with shims. Neck joint just isn't tight enough. So, use a drill press to make straight holes, and don't use shims.