Can a defense attorney depose an applicant for protective order? Never run into this before.

Never heard of it being tried but, given that discovery control plans limit the period to conduct all discovery and that period ends "30 days before the date set for trial, in cases under the family code" and given that the hearing/trial for a protective order must be set within 14 or 20 days (depending on jurisdiction) of the application, I do not think they could compel a deposition.