No, a cheap, weak rim will bend under a 200+lb rider no matter what the spoke tension is. The crappy alexrim wheels on my SE lager repeatedly came out of true, despite being retensioned several times under my 200lbs of body weight, but my 140lb exgf has had them for 3 years now and has not had to have them tensioned or broken a spoke the whole time.
The load on metal spokes is tension, not compression, so if the rim itself is bending under the weight of the rider even tension won't keep the spokes from breaking or coming unscrewed anyways.