Mary Allred was Solomon's first wife; their children wre Early, Solomon, Elizabeth, Rebecca, Sallie and Pollie. Sometime between 1820 and 1828, he married (2) Rachel, but I've seen no mention of her last name.Their children were Isaac, Ruth and George (as you've seen in the Census).
Yes, Polly Hays was his daughter, the last one with Mary Allred.You mention his absence in 1850, but the appearance of later Hays children. Who knows, maybe her husband was in California for the Gold Rush!!