Because your cat had recent DKA and is still in the process of recovering, it's important not to skip shots if possible. Because lantus is a "slow" insulin, often after they eat the blood sugar can increase for a couple hours after the shot. So shooting on a lower number is scary at first, but is something that experienced people do regularly.
That said, -AT THIS POINT- because he had DKA, he might have more swings, and risk for hypos, so you do want the BS to be more in the blues. If you shoot half a dose for a green number, often that reduction is enough to keep them from going hypo, and to keep the blood sugars from going too high during the day. If you are feeling nervous about half the dose, go even lower than that and see what happens. But shoot something. No insulin may cause his blood sugar to be skyhigh at next shot time, and may allow ketones to come back. As always, have a hypo toolkit ready and be comfortable in using it.