Sorry, I was thinking of another rod. The slabseeker does have guides and rings for a reel. Is there any reason why you would not have purchased it for fly fishing instead of tenkara?
It so happens I have a Zebco 12' Slab Seeker that I bought before tenkara rods were available in the US. I just pulled it out and weighed it. It's not really a fair comparison, because it was broken during shipment when Cabela's sent it to me so I had to repair it, and the repair did add some weight, but as it stands, it weighs 8.2 ounces.
The cheapest 12' tenkara rod ($50) I've purchased weighs 3.3 ounces. You can guess which one I'd rather cast all day long. My favorite 12' tenkara rod weighs 2.6 ounces. With it I can cast 8 pound test fluorocarbon spinning line as if it was a fly line. Turns over a small wet fly beautifully and lands without a ripple on the water.
I'm sure your new, unbroken 10' Slabseeker weighs less than 8 ounces. I've got a sweet little 10' rod that I sell. It's not designed as a tenkara rod but it works very nicely as one (for smaller fish, that is). It weighs 2 ounces.
The Slabseeker is fiberglass, which not only makes it heavy, it makes it whippy. When you wiggle it and stop, it keeps wiggling for a long time. When you wiggle a tenkara rod, it stops wiggling right after you do.
I really don't mean to give you a hard time, but I am continually surprised that guys who would pay $300 for a fly rod without batting an eye (or $400 or $500) honestly ask if they can use a $20 rod for tenkara. A tenkara rod is just a technologically advanced as a fly rod, and is designed to do things a fly rod can't do, like cast a light fluorocarbon line, absorb the thrust and fight of a 20" rainbow, and still land it with 6x tippet without needing a reel and drag, not to mention being 12 feet long and weighing less than 3 ounces. Most of the ones for sale in the US go for about $150-170. OK so they don't have a reel seat and guides. Just how expensive are a reel seat and guides anyway?
I wouldn't mind so much if I saw people ask on fly fishing forums if they can use a $20 crappie rod for a fly rod but you never see that.
I guess I better actually answer your question. Yes, you can use your Zebco Slabseeker as a tenkara rod, but it won't be a very good one and it won't give you a very good understanding of what tenkara is all about. Seriously, it's like fly fishing with a spinning rod. Sure you can, but why would you want to?