I'm really not seeing, "Well there are never any ships orbiting Vulcan so we'll probably be fine," cutting it from a legal or moral perspective.
Try to remember, though, that this is an emergency situation, so the fleet's probably booking it for Vulcan like a squad of police cars racing to the scene. They'd have the subspace radio equivalent of "sirens blaring".
Of course, if it hadn't been for Narada's drill jamming all the comms they probably would have gotten approach clearance from local Vulcan authorities too. The silence from those authorities was probably assumed to be related to their seismic troubles until the Narada opened fire on everyone.
I'm still not seeing enough safety features to justify the risks warping into a solar system. The orbit of a planet is tiny compared to warping to the edge of the Oort Cloud for example.
True as that is, starships are even smaller. The chances of accidentally warping into a collision course with another ship are infinitesimally small, even if the ships are dropping out of warp directly in an orbit that is used by commercial traffic.
Something to keep in mind: if you have 100,000 ships, satellites and space stations in geostationary orbit, anyone warping into Earth orbit could succesfully avoid a collision by dropping out of warp just 200 kilometers ABOVE geostationary orbit. You can go to impulse power and drop into geo, or bypass the geo belt altogether and drop to LEO.
Heavily populated worlds probably have a number of desginated orbital altitudes and inclinations that is set aside for arriving/departing space vessels and that local traffic avoids as much as possible just to keep everyone safe.