I'm not sure specifically at the LV bus station, but right next to it is the Union Plaza and right across the street is the Golden Nugget - 2 major hotel/casinos in downtown LV. I'm sure they have cabs.
Sometimes I see a bunch of cabs waiting in the pull off area. Other times none. The Bus station is on "Main" street downtown. There are a bunch of hotels in that area. I would not worry about a cab unless you are arriving in the early morning hours.
If you're laying over at LA Union Station from 1 PM to 10 PM, you totally have time to go see some of Los Angeles.
Disneyland is too far. But the Metro Red Line and Gold Line connect directly to Union Station. So, for example, you have time to visit Universal City (which has a Red Line station) for a few hours if you like that sort of thing.
I visited the La Brea Tar Pits during an LA layover once (with all my luggage stored at Union Station); it was a bit more work than Universal City because you have to actually change to a city bus, but it wasn't half bad.