Sorry, a bit more precise: Is casper the base for the Smart contract executor?
No... smart contracts are already a reality without Casper.
https://etherchain.org/contractsSmart contracts in a real world setting that must scale can not exist without Casper.
The virtual machine for smart contracts runs, but any sort of real world scaling of the virtual machine requires Casper.
I have explained why Casper can't possibly work and my point is unarguable.