Glass tanks are designed to have all the weight resting on the rim, with the bottom pane raised. This is supposed to reduce the risk of cracking the bottom pane.
As long as the entire rim is resting evenly on your cabinet, you should be fine. The styrofoam under the rim is supposed to crush down to conform to any minor uneveness of the cabinet. If you run a card along the rim, there should be no gap at all around the whole rim. If there is any gap, you need to level the cabinet (shim or sand) to prevent pressure cracks.
A 1 cm out of level is *probably* OK. Although to be doubly safe, you might want to do better than that. <I aim for less than 1/4" or 0.5 cm when setting up my tank.> And as the previous post said, make sure the floor can support that weight .... else the floor will sag & shift and the tank will get really out of level over the next weeks/months and give you problems.
Also, if you have a lot of rocks in the tank, most would suggest putting the rocks on top of egg crate (a plastic grid) to spread out the load & minimise the stress on your tank bottom.
80 gal FW with 30 gal DIY wet/dry/sump.
9 fancy golds, 1 hillstream loaches, 1 rubber-lip pleco (C. thomasi), 3 SAEs, small school of white cloud minnows, planted.