I'm not sure which ones you're referring to, but the NVDIMMs I'm familiar with [0] are are normal DRAMs with an additional hold-up supercap, controller, and flash. When power goes away, the controller streams DRAM contents to flash. Linux block device Drivers [1] exist as does some filesystem support [2] for ext4fs.

[0] http://en.wikipedia.org/wiki/NVDIMM

[1] https://lkml.org/lkml/2014/8/27/674

[2] https://lkml.org/lkml/2014/3/23/121