There's enough places for microbes to hide from radiation. On that short of a mission it wouldn't be surprising to see microbes. There are various microbes that can withstand the nominal radiation there. Would be much harder to survive the Van Allen belts and CMEs, but it is possible. If we were talking about a 100 year mission, that would be more surprising. Even hardy microbes don't like extended stays in vacuums and have to go into a hibernation state. There are bacteria that can survive for decades in a vacuum and low temperatures.
how short? because i thought the timeline we're talking about is that the Roadster is not going to run into any planet for as long as they've run simulations for, but it's theoretically possible that it might, at some point, hit something.
Disclaimer: not a biologist