I doubt there's a connection between the two cause of the hard vouch. Udell is not someone who would allow his buddies to do something like that for him. He's a busser and likes to distance himself from his teammates. A hard vouch is the complete opposite of that. So if Naomi flips scum, it doesn't incriminate Udell imo. I strongly doubt he'd allow Naomi to vouch for him like that if they were a town.
And tbh, for Naomi herself, her vouching for Udell makes her look better. I've some knowledge of her playstyle and she is not the type of person to strongly vouch for anybody as scum. She's more reserved and quiet, trying not to get any attention to her. She doing that gives her some townie points from me.