Can't use preorder money like that, its fraud. In the same way I can't sell you a computer delivered in 6 weeks and gamble it all in the mean time.
Well if or if not their pre-orders were done according to the law is one thing, but no, you can not say HOW a company uses pre-order money that specifically. If the units cost $400 to make and they took in $1200 they certainly could keep some in BTC.
Aah but there is the gamble. Few scenarios:
1) Costs them $400 to make, took $1200 and invested the rest. As long is everything is reasonably assumed, this is okay to invest the $800.
2) Thought it would cost them $400 to make, took $1200, ended up costing $800 but they'd invested $800. BIG PROBLEM, BIG BIG PROBLEM [regardless off what happened to the investment]
3) Thought it would cost them $400, took $1200, invested $1200. Stop. Go directly to jail.