Is that just because you don't want to invest the cash in Mournfangs and want some stand-ins? If so, then sure go for it. I once used an old dwarf flamecannon as a thunderfire cannon with a techmarine in 40K...so I see no problems with stand-ins. However, if money is no option I would recommend the official Mournfang over Dragon Ogres, but that could be just because they are amongst my favorite miniatures. Some fo the most impressive cavalry in the game in my opinion.
To be honest I don't like the mournfang miniatures and I'm doing a WoC army anyway so I thought two birds with one stone and it would save some money as well.