Certainly my friend, there is no substitute for a good diet and lifestyle - and the items in the Gerson therapy surely are wonderful things to do for cancer and more. The Gerson protocol is a very good one and it would be very stupid to abandon it and just take oleander.
No one should ever try to substitute any single supplement, drug, plant or whatever for an overall cancer beating lifestyle and diet. Better by far though to follow a protocol like Gerson and add the oleander and perhaps some other good cancer fighters. Iodine and colloidal silver are two of the best.
Having said all of that, if it came to a showdown between Gerson and oleander, I would choose oleander hands down.