To know if they are setup tubeless, unscrew the nut holding the valve stem a little bit and push the valve in. If that releases air, they are tubeless.
To add sealant, your valves should have removable cores. Remove the core and squirt sealant of your choice -Stans two ounce bottles work nicely for this. As for how often you need to add sealant, it depends mostly on weather where you live.
Some people have to replenish sealant every month. I have taken off tires after three months and sealant was still good. I have no experience with the Vitoria sealant, just Stans. Keep in mind that Stans will eventually congeal into the "boogers" or "Stanimals" so you'll have to pop the tire to remove residue.
If you do remove the tires, you may need an air compressor to seat the bead again.