I'm come to the conclusion that it poses no danger at all... as long as the proton beams are shot in a sequence of small pulses. If it's done like that, it'll allow any formed micro blackholes to safely dissipate via hawking radiation before the next sequence of collisions occur.
However if the beam is continuous without pause, I feel the risk of a stable micro-blackhole forming statistically increases over time. This is because there's a very small chance that a group of micro black holes may form within immediate vinicinity of each other upon the collisions, absorbing each other and then grow instead of decaying as intended. But this assumes that the collisions produce a high volume of micro black-holes in an immediate vicinity of space and time. Also such a process would take a long period of time of 'feeding' to achieve, and any interruption of the beam would likely cause the micro black hole to dissipate beforehand. It's hard to say really, as my knowledge isn't great with this aspect of physics.
