Nope, I havent compiled MRTG......but I do see now that RRDTool is already in the ipkg package streams, so I guess this will be my choice :-)
Good call. RRDTool rocks. It's actually (IIRC) done by the guy who wrote MRTG.
I think the big problem would be that MRTG is writen partly in perl. So you would need to port perl to the WL. Once you have perl, getting MRTG is fairly easy. But it's been a while since I played with MRTG.
However RRDTool is just the database + tools for the data, there is no collection tool included, MRTG would collect the data for you via SNMP. You can easily setup some little scripts to feed data into the RRDs. Once it's in there you can generate png graphs using rrdtool.