He says he doesn't know anything -- and I believe him He certainly fooled Tom too

Roth's inside man Fredo's own words, lie after lie, he was feeding Michael
1. I haven't got a lot to say Mike.
2. I was kept pretty much in the dark.
3. I didn't know all that much.

Let's stretch what was seen onscreen and give him the benefit of the doubt that Roth misled him, he really thought his little help to close the deal fast -- in Roth's favor against his own brother for “something in it for me -- on my own” would be good for the family and he didn't know it was gonna be a hit

If that's all it was,
1. why bring up the Donship?
2. Why would the Donship be even an issue?