They don't even need to be able to win. An existing "legit" patent holder might choose to simply throw lawyers at as a tactic to delay or defeat a potential competitor. In that case, it comes down to a cost/benefit analysis for the would-be litigator.
Also, any companies contributing to the NETVC standard are required to declare IPR, which is not the case for MPEG standards.
I'm not sure what this means. A royalty-free video codec basically has a bullseye painted on it from the perspective of existing rightsholders. The only reason such entities might exercise restraint is because the cost/benefit analysis doesn't support litigation. Even if they don't think a competitor codec is a threat at the outset, there's nothing stopping an attacker from just sitting on the sidelines and waiting until the threat profile (and depth of infringers's pockets) becomes clearer. I.e. the "submarine patent" model, except it could even be a known patent in this case.
I think Daala's development process (and IPR disclosure policies at the IETF) reduce the risk substantially. However, this is not automatically true of any RF codec.