Lots of folks have been running semis on 29" rims/bikes for years now. Two of the first 29" tires available here in the states could be considered semislicks: WTBs Nanoraptor and Vulpine. I'm currently using the latter on a Stan's Arch EX (set up tubeless) on the rear of my 29er that has been relegated to commuting and mixed terrain rides. It's sub 600g IIRC and rolls really well. I ride some trails that have plenty of loose dirt, and it works great on the back - limited slippage.
Similar but a bit faster and lighter than WTB's now extinct Vulpine is Kenda's Race 24Seven. It's a DTC tire available in tubeless compatible casing, and it rolls really well and still gets good climbing traction in the dirt.
Because I ride these tires on loose soil sometimes, I only use them on the rear, @ ~30psi (for my 185lb riding weight). Using these on the front would mean dumping the bike in turns, and that's not too fun. I use micro/small knob tires up front (currently a 2.2 Ikon) since rolling resistance matters less, and traction matters more, on the front.