How can I achieve a straight ridge line when taping a vaulted ceiling?
There's one key to remember when doing ceiling ridges and other obtuse angles: The planes of the ceiling determine the position of the corner line.
So, is your ceiling flat? If you run a straightedge across the small gap at the ridge to the other plane all along the ridge, does it draw a reasonably straight line? If so, you're golden. If not, you have some thinking to do, because the outcome will necessarily be a compromise. You can pull down some drywall and shim it, or you can carry on and hope you can fix it with mud.
To answer your specific question, you should be able to work one section at a time, abutting the tape for each section.
Here's how I'd approach it.

Prefill. Hangers rarely get those tricky ridges tightly closed, so you need to create a base for your tape. Skim the planes to fill the ridge gap from one side, and let that dry. Then do the other.
Once you have a naturally-positioned line, pre-fold your tape and lay it in. Work one side and then the other, just like for prefill.
Once that's all done and dry, see what you see. Look at it from one end, and look at it from all critical areas of the room. How does it look?
Make any adjustments. If you see a wiggle, fill the depression and taper it out. Use your widest knife or a skimming blade, pulling down from the ridge. Work the mud up slowly so you don't have to carve it back down by sanding.

I'm not a pro taper, but I've mud-dled my way through many jobs and have seen countless jobs done. That's the gist of it. If it looks good from the floor, it's good.