The seat will easily be crushed in an impact if they are installed like that. The following figures are from an article in Track & Race cars from a test by Schroth (who make harnesses). They did a standard FIA crash test, which is a 31mph impact with a stopping distance of 16inches. This produces a decelleration of 30G.
The load on the lap belts was 3,100lbs each side. The load on the shoulder straps was 1,550lbs each. That caused the adjusters to move up the chest by 8inches due to the belts stretching. 1550 lbs would easily crush the shoulder strap holes in a seat - they are not designed to stand up to any force, they're only for locating the belts. Also bear in mind that test was using a full 6 point harness, and the anti-sub straps took 1320lbs of force each. If you only have 4 point harnesses (which I would never use) that force will be transferred to the shoulder straps too.
And that was only a 30mph impact (albeit with a short stopping distance).