The fact that system like this still exist isn't a good thing. We should be at a day and age where people can be looked at equally, regardless of their social status. However, I never really find it appropriate for other countries to get involved with traditionalist systems. It is hard to judge from an outside perspective. So yes it should be raised. But unless a cooperative decision can be made, I don't know if it is worth forcing change.
The caste system is, by definition, an internal struggle within India and other countries. Unless people are being mass murdered in the caste system, the UN has no right to get involved in the struggle to do away with the caste system. Plus, the caste system isn't supposed to be in government and it based on ancient religious principles. Matters of religion shouldn't be taken up by the UN in the first place.