Sure. When it's an option, I'd do it too. And when they're billing you, hiring a bucket truck will absolutely be in their safety plan. Might even be law, or required by their insurance. The question in my mind is not what a rigger will recommend to you and your pocket book, it's what he'd do himself on his own dime, if rigging a forestay wasn't an easy option. Since, you know, I'm doing all my work on my dime.
My discussion with an experienced rigger was about replacing 21-year old rod rigging. I expected I'd need to have a boatyard pull the rig. It was the rigger who said I could avoid the hassle and cost by working on my boat alongside a small floating dock--No bucket truck. He said it could be done at the slip by a rigger ascending the mast. He would keep the mast guyed with own ship's equipment as the standing rigging was replaced, piece-by-piece.
The rigger's safety plan did not involve extra equipment or costly procedures, but it did involve keeping the mast guyed in all directions at all times.
I do a lot of my own work, including plumbing, wiring, installing refrigeration, water and holding tanks, a windlass, radar, and below-deck autopilot, but I have my limits. My decision to have a rigger do the work is about getting a qualified rig inspection, as well as a qualified rod rigger and his equipment to do the job correctly. I've known this rigger for over 16 years and trust his expertise and ethics.
Bottom line: A spinnaker or genoa halyard will temporarily guy the mast when the forestay is removed. Leaving the mast unstayed in the forward direction is not an option. BTW, I've always seen this rigger use a safety line, like an extra halyard, when ascending a mast.