Illegal in Utah
Sure, it happens all the time here. All too often the center turn strip is used as a defacto merge lane to get into traffic from the opposite side of the road, but Utah traffic law doesn't allow for even a bit of merge type use. When entering the road, the law here calls to simply cross the strip and into your lane; if you can't pull into traffic without using the center strip, you shouldn't pull into traffic at all per our traffic law.
I think most of the illegal use I see is from ignorance of the law, rather than deliberately breaking the law. My overly cautious model citizen spouse received one of her two lifetime traffic warnings for using the center lane to merge - she had no idea.