Solarcity was clearly a great example of Elon's ,,no investor left behind'' philosophy: if he promotes a company and gets investors to invest in it, he is doing whatever he can to make sure that they at least don't lose their money (by merging it to a bigger company he controls), even if it wouldn't be the best financial decision.
So far this strategy has been working quite well for both him and the investors.
Frank being against Elon speaks less about Frank and more about Elon in my eyes.