Yes, you can use them as a normal Troops choice if you like. However, note that they don't have the DEATH GUARD keyword, so if you include them in a detachment, that detachment will no longer qualify as a "Death Guard detachment" and so won't get any of the associated abilities.
An alternative is to have a dedicated detachment for your daemon forces so your Death Guard keep their bonuses, or include the Nurglings as an Auxiliary Support Detachment, though this will cost you 1 CP.
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