You're talking about last year's stalks?
They do seem sturdy and I used stalks I saved in the shed to support tomatoes. They did well for 1/2 the season, then during a summer storm (it was an exceptionally heavy one with a couple of small tornadoes landing in a nearby area) after the toms had grown quite big, so we're talking late July~early Aug, they snapped in the middle and left me scrambling to keep the toms standing!
Combination of soaking wetness, weight of the tom vines, and the wind did them in. They also got scraggly looking with black sooty mold like stuff. Didn't affect toms (which I was worried about), don't know about morning glories. On the other hand, morning glories wouldn't be as heavy as tom vines... then again, my morning glories grew quite lush, completely covered 7-foot arbor trellises, and almost pulled down the cheap hollow metal trellises in the same super-windy summer storm.