First, Dawn is a detergent, not a soap. Research has not been done on using it as a pesticide but certainly it is not labeled as such and anecdotal evidence can site many cases where it burns the tar out of your plants. There are no recommended dilutions. Vegetable oil is also not the same as horticultural oil and shares the same problem of how much to dilute. Oils are not to be used in hot weather as they famously fry plants. Even Neem, which IS labeled as a plant insecticidal oil has cautions about the conditions under which it is used. Flea beetles are particularly difficult to control as they are so fast and generally feed most before dark or early am before most of us are up. Pyrethrins are the recommended organic control, koalin clay (on some crops) and rotenone if you have any left over. Carbaryl (Sevin) and malathion are the conventional control. Spray just before dark. Pair this with good weed and post-harvest clean-up and a spring turning of the soil to expose overwintering insects. Consider the use of row covers:
 https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/3104/3104-1549/ENTO-251.pdf