Assist does not work on the first or any shot in AF-C or when in AF-A when the camera senses it should auto focus.
The red grid pattern is hardly seen by subjects, it is low energy and not bright and accordingly, I have never heard of anyone complaining about it or even mentioning they saw it.
AF Assist works differently on different models. The D7000 uses it with any focal point while some other cameras only turned on when the center FP is active. One of the conditions for its activation is being a FL between 24-135mm. Stan St Petersburg Russia