Welcome, Eliot, to the OEM forum.
What you have there is a complete electricity meter, you could feed ONE of those into an emonPi using the pulse input, but your emonPi won’t accept a direct voltage or 4-20 mA input, it is designed solely for a current transformer.
I haven’t yet checked the full data sheet of that, however if you are looking to have something like that, I suggest you look at those that have their output on a data bus, that you can send more or less directly to emonCMS.
You mention CTs in the plural, I think we need a little more information on your proposed setup to give you the best advice. Will yours be single phase or three-phase installation, and how many points do you want to measure independently?
I think - but heavily dependent on your answers - that if you do want a complete meter and you want to measure several separate circuits, you probably need to be looking at something like this: PZEM-016 single phase modbus energy meter
If you search here for “MODBUS meter”, there are several discussions about different models.
However, coming back to the original question - can you use a ring-core c.t, then yes you can. But you do need to take some precautions. A c.t. should never be left open-circuit, it should be short-circuited or it must have a proper load, called a ‘burden’. Some c.t’s have internal protection to prevent danger should they become disconnected, but you shouldn’t rely on that.
I had found a range of three small ring-core ones from RS Components, but there’s a problem - the web page and data sheet have conflicting information - the RS website is wrong (confirmed in a phone call). They are suitable to directly replace our standard c.t. and connect directly to an emonPi, there are 3 ratings: 25 A, 40 A & 50 A: https://nz.rs-online.com/web/p/current-transformers/7754909 is the 25 A, https://uk.rs-online.com/web/p/current-transformers/7754903 is the 40 A. & https://nz.rs-online.com/web/p/current-transformers/7754912 is the 50 A. (You’ll need to fit a plug, and those are not protected, they must not be open-circuited.) Those are significantly smaller than our 100 A split-core c.t.