Camera clipping doesn't work on CObjects (which MTA uses for all custom objects), wherever they're placed, I believe. Writing your own manual camera clipping isn't too hard, and raycasting - processLineOfSight or isLineOfSightClear is the way to do it. The principle would be to cast a line (or four lines, one from each corner of the camera) to the player (or whatever the focal point of the camera is). If the rays hits something en route, move the camera a bit in front of that point it hit. Combine that with some smoothing so the camera doesn't jolt around too much and you've got a reasonable first start. In practice it's a bit harder than that as there's some odd edge cases to catch.
A better solution would be for MTA to hack GTA to support objects properly, which I'd guess would be quite easy.