Using the attached resource pack for an example, the item model for the soul/normal campfire is identical to the block model. This has elements for the fire using the "shade" tag, set to false. Despite being set to false, the flame portion of the model responds to lighting. This is most obvious in the GUI/hotbar, where the fire is noticeably darker than it is when placed. Panning the camera up and down while holding the campfire also causes the lighting on the flame to change slightly.

This is in contrast to the block model, where the flame portion of the campfire respects the "shade" tag. The item model doesn't need to have emmissive lighting or anything, but the shade tag currently seems to do nothing for item models.