It does not, no.
The SPFlash utility is meant for flashing the OEM image and partitions and communicating with the phone in a special lower-level mode that makes it (almost entirely) unbrickable and able to be recovered. Secure data erasure is a non-goal of this tool, from what I can tell from how it is laid out.
In terms of data recovery, a consistent write of 1 or 0 is easier to recover than (semi)random data written over it, so reflashing the user partition and maybe dumping a bunch of random-filled files on it between reflashes will be a much better secure-erase process. You can generate them on Linux with something like this: head -c 1G </dev/urandom >myfile