I am currently using a pair of these Leviton dimmers with my Harmony 890 which is a preferred way of controlling them since they are usually being used in conjunction with TV watching. I would love to also integrate them with the smartthings hub since they double as repeaters as well. As of right now smarththings is not finding the devices. is that because they are already paired, or are these things unrelated?
any way to use the dimmers with zwave and harmony?
You are right that smart things is not finding them because they already belong to a different Z wave network. Zwave devices can only belong to one zwave wave network at a time
The harmony 890 was discontinued by the manufacturer about seven or eight years ago. And the firmware was always limited: it could only control zwave light switches. 
Although it is sometimes possible to add other Z wave devices to a smartthings network as a secondary, that will unfortunately not be possible in this case.
You would have to replace your Harmony 890 remote with a Harmony hub and a Harmony companion remote. Then you could use the official smartthings integration.
The switches by themselves should work fine with smartthings, but they can only belong to one Z wave network at a time, and because of the Limitations of the 890, there’s no way to combine it with smartthings.
I wish I had a better answer for you.
Is your Harmony device an 890 or an 890 pro?
Also, do you know the last time the firmware was updated? Apparently logitech made some changes to it back in 2006 which limited each remote to eight devices and did some other things to it as well. So that can make a difference as far as what might be possible.
Can you explain exactly what you would like the remote to do? Because I do think you might be able to accomplish the same thing with a current harmony device and the official integration with SmartThings, but it would mean buying new equipment, and I don’t know if you have any interest in doing that.