I'm not sure about taping plaster cracks. I know with drywall, you do this with butt joints and such. In any event, normally, plaster cracks are dug out a bit deeper to allow the new plaster to 'grab' onto something. If the area you're describing has failure beyond just the crack itself, again, normally, the damaged area is removed and a 'mesh' is tacked to the lath for the plaster to grab onto.
FWIW, I'm no expert on this. I would go to Tuscany Village and click on the 'Discussion Forums' URL at the bottom of the page and post your question for Bob Ewing to answer. He's a Plaster Restoration expert, and then some, and has learned from the Master. He'd be happy to answer your question. If this isn't done right, in 6 months, you'll be back at it again. Best of luck