Problem is the grapihcs if hes wanting to doffing, which is fine, but the problem is the game pull, all I can say is for him to install it, if the program installs, then it souldnt be to much of an issue.
I don't think it would be the processor itself that would make or break the performance (always been my experience that with very few exceptions RAM is much more important). I have an i3 in my two-year old Sony Vaio notebook and it runs STO decently enough on mid-range settings (I had to downgrade my graphics driver recently because something about newer drivers conflicts with S7 right now though). I can DOFF or simply play the game in general. I would think if DOFF is all he wants to do then he should be fine though.
Basically, I would make sure the computer has plenty of RAM. Between 4-8 GB is enough, You don't want less than 4 GB because no matter your total installed amount of RAM, the integrated video card will take from the system memory. Basically, if the processor is not the best, having less system memory equals less overall system performance. When it comes to RAM better too much than not enough (of course certain operating systems won't see more than 2 GBs of RAM, but I don't think most modern computers have that problem).