Running one wheel with clincher and one with Tubular
If flat takes you out of the race, then there is no big reason not to do this. As noted, the biggest reason not to is having to carry more flat protection.

You might even decide to purposefully choose different tires - a bit heavier in the rear for a bit of puncture protection, something that adapts to wet a bit better in the front for steering when it starts to drizzle, etc.

Bottom line, not a safety concern.

Happy Riding.