It won't be as cleansing and the lather would be different since saponified tallow is nowhere near as cleansing or bubbly as saponified coconut, but depending on the outcome you wish to achieve in your finished soap, that's not necessarily a bad thing, and can actually be a pretty good thing. You never know until you try!
One of the shaving recipes that I've been studying lately is this one here:
http://bubblelovesoap.weebly.com/blog/the-art-of-wet-shaving
It uses 40% stearic acid, 40% tallow and 20% shea butter, about 10% added glycerin, and a 60/40 KOH to NaOH ratio, and that's it! Well, other than water, that is. Notice that it doesn't contain any coconut or PKO or babassu (the really high-bubbly/cleansing oils). And if any of the comments below the recipe are to be believed, people who have tried it seem to really like it. I myself will be trying something similar hopefully some time next week for experiment sake.
And there's also a very successful artisan soap-maker whose shave soaps seem to have garnered a very loyal fan base amongst some of the wet shavers on the different shaving boards, and she doesn't use any coconut, pko, or babassu in her formula either.
So, what I am saying is- go for it! You never know unless you try. And let us know how it came out!
IrishLass