How much they have give them ? 15 millions of $ ? Do we need to think this is the same for Oxyde ? Chrome engine ? TryArch, Crytek etc ?
Do they have put money on the co-joint project with Dice who have work on developping Mantle and make it a reality ? Thats sure.. i dont think Dice will have get so free time developpers for work on it just for the fun anyway. Cost have certainly be more shared that we can imagine.
When you have a project together, or working on a project together, everyone put time and money on the table.
I dont see them come to Dice and say, " hé guys, here's Mantle, now you will work for developp it with us, but this is at your own cost." Cost have been calculated, feasability, times for realisation, number of developpers who will work on it on different phase of the project ( developement, test, port in the Frostbyte Engine, test, modficiation ).
You dont come with something like that and ask them to work in their free-time, the week-end.