The concept might have been used, but I cant think of any examples where other franchises flat out refer to them as "space marines". Like it or not, but the phrase "Space Marine" is heavily associated with the Games Workshop product. I was actually surprised this hadnt been jumped on by GW already by now, as their lawyers are quite ferocious in defending their IP. Actually building lego drop-pods really raised an eyebrow for me as well, there was no way they were going to let that slide.
Best of luck to Hjmediastudies getting this sorted out and the Cuusoo project approved by Lego. I voted to support. :)