That seems to me like a little bit of overkill. You should be able to find a single band 2 meter mobile radio for next to nothing. Seems to be a shame to use an 857d for a basic task like that.
But yes, it will work. I did something similar (with an old Radioshack 2 meter mobile) when I lived in a fringe area. I used an MFJ sound card interface and the paid-for AGW Packet Engine, which seemed to work better than the free one (the author said they are completely different). Ran that through UI View and it worked great.
One advantage to the FT-857d might be a more sensitive receiver than an old mobile.
It is a shame to use the 857d that way, but I ordered a D710a for the truck and the 857d will end up doing nothing for right now if I don't use it for this. Eventually I do want to purchase a dedicated 2m for the igate station, then the 857d would become a base radio for my cabin up north, but for now it will earn its keep as an APRS gateway
I'm going to set it up this weekend and try it out, should be interesting.