I'm wondering, have you actually talked to Ulfric about his cause, or listened to Galmar or any of the generic commanders in their camps? I'm not advocating taking their word at face value, but actually entertaining the possibility that they are genuine.
Of course, I'd recommend to not take Rikke's word at face value either(whom you paraphrase rather accurately here). As a Legion Legate, she is a very biased source and her words regarding Ulfric and the Stormcloaks have to be taken with care. As a rule, you shouldn't assume that the negative* the sides say about the other one and its members is true without evidence to back it up. And even then you have to measure it up against evidence to the contrary, if there is any on that specific topic.
In short, don't assume pro-Empire people are honest or accurate about the Stormcloaks, or vice versa. There is too much value is giving your enemy negative propaganda. Dismiss anything that does not have evidence to support it against scrutiny.
*Edited for clarity. If a pro-Stormcloak source says something positive about the Empire, or a pro-Empire source says something positive about the Stormcloaks it has quite a bit of validity, given that there is no intrinsic value in lying about it for the ones involved. It should still be measured against evidence though, if any exists.