Reginald Braithwaite has some interesting comments on Twitter: https://twitter.com/raganwald/status/1102966537869094913

Basically, in his experience being on a bike amongst the support vehicles isn’t a problem; what is likely to be a problem is if the leader of the second race catches up with the first race and gains an unfair advantage from slipstreaming with the earlier riders, negating the usual disadvantage of breaking away from the peloton.

I guess that would apply regardless of the rider categories if the two races.