[tss68nl]

Vacuum evenly attracts body tissue and air, but as air is lighter (thus accelerated faster) and has less resistance to flow (less viscous) the blood splat will not be very large.

It is true that some of todays ammunition will induce more blood to come out on impact, but in general, blood will really only come out after impact slowly.
Even if it would create a 'blood fountain' it would still be catched by the uniform. We are talking almost a centimeter of wool-like uniform here, once the bullet is through, the gap closes immediatly.