Only Muslims are allowed inside masjid al haram regardless of whether you want to do umrah or not and regardless of the type of visa you hold.

The pilgrim doing Hajj or 'Umrah may enter through any gate, but when he enters the mosque he should enter with his right foot first and say what is narrated for entering all mosques, and send blessings upon the Prophet (peace and blessings of Allaah be upon him), and say, Allaahumma aghfir li dhunoobi waftah li ...