I remember doing this with VW 16vs back in the day. The exhaust cam mod had more duration and greater lift than the intake, even moreso than the vaunted Euro intake cam but required some fiddling to get it to work.
When oriented as an intake with no modifications, it was about 3.5* retarded in relation to a regular intake cam. To bring the centers back to a "normal" state, you had to run an adjustable sprocket on it to dial it back. The problem was, the exhaust cam was driven by a belt and at the opposite end, the intake was chain driven by the exhaust inside of the valve cover.
The other caveat is that you had to machine the cam gear nub off of the cam to be placed on the intake side as well as round down the distributor drive. The cam physically wouldn't fit otherwise. I think this is still in the 16v forum of the Vortex somewhere.
What I've found in my limited research with Subarus is the opposite: the intake cam is more aggressive than the exhaust (WRX) with the exception of the STi set which is bigger all around, especially in the exhaust.
Obviously you'll have to fiddle with gear orientation and use a set of adjustable sprockets to get it within spec. The other problem lies in the fact that there's four cams (4x the cost) to fiddle with and they're not all that easy to get to. That and setting lash with buckets, VW's have hydraulic lifters...
I would say the more cost effective option is to go with a cam for your setup that already exists unless you have unlimited time and funds to play around with a maybe.