I think a good example for the original question, does ODI form relate to Test Selection, is Michael Bevan.
Bevan was tried at test level, and was hugely sucessful for a short time before a horrible run around 97/98, whih was when he was dropped and subsequently never given another chance, despite fantastic ODI and FC cricket form. Of course, he fell into the unhappy category of an ODI specialist, and I believe he peronally rues this label. Just like Langer, the Test Match specialist, who would love to have a go in a ODI shirt, but will probably never get another chance.
So, looking at the trends of Australian cricket selectors at least, ODI form does not directly relate to Test match selection and vice versa.