The basic Amelanchier does come true from seed, but Ballerina is a cultivar - information available suggests its grafted onto a rootstock, so not at all sure what you'll get from seedlings. They may be the same as Ballerina, but not grow so well on their own roots, or not be the same at all, be interesting to see. Usual method of propagation for cultivars, in order to duplicate features, is layering or softwood cuttings.