Yes you can use a zero-offset post, nothing wrong with that. I will also add onto 2old2mould's reply that full suspension bikes sag more in the rear when you're going uphill, since the weight balance shifts rearward. MTB seat tube angles are getting very steep because the terrain is often steep, which geometrically rotates the bike back and puts the saddle more rearward, and the additional rear suspension sag causes the saddle to shift rearward as well. So it's not that 78deg STA is typically a good pedaling position, it's that 78deg STA ends up being more like 74, 75, 76deg when climbing.
I'll add my experience, that I also like the steep STA of my FM936. I also have a CFR707, and run the saddle in the middle of the offset post. It's STA is still steeper than a traditional road bike, but not near MTB steepness. But for me, it works very well. Seatposts are cheap though, nothing wrong with trying out both kinds. You can also just slam the saddle all the way forward on the offset post, and even though it's not safe to run on rough stuff, it'll give you an idea of what a zero-offset post would feel like.