If a sex offender sees his daughter prior to court, can you use sex offender charge in court?

Don't listen to him. Now you are stupid if you allow him to be alone with her. Presuming you are not stupid, just seeing her with you does not ruin anything for you. As for custody, there is no way the court will allow him to have custody of her. This may be one of the few instances where the court would approve your moving out of state with the child because there is no way he can provide a home for her. All you can do is ask.

Evidence of a parent being a convicted sex offender is clearly and unmistakably relevant and admissible evidence as to the issue of whether sex offender parent can have contact with his child and the manner of contact with the child. The fact that a parent has allowed the child to spend time with the sex offender parent previously does not make the sex offense conviction a moot point. In Utah, if the parent has an enforceable order awarding her sole physical custody of a child, then unless the decree of divorce or the decree of paternity provides otherwise, the custodial parent can relocate anywhere she wishes within 150 miles of her current residence within the same state. If the custodial parent relocate to another state, even if it is less than 150 miles away from her current address, or if the parent moves more than 150 miles away from her current address, then Utah Code Section 30-3-37 requires that parent to notify, if possible, the other parent of intent to relocate 60 days in advance of relocation.

File your intent to move with the court vive him certified notice. Yes bring up sex offender stop letting him see her.

Of course you can still bring up the fact that he is a sex offender at the hearing. It's definitely relevant to the issue of custody. However the judge may question why you would volunteer to allow your daughter to spend time with him knowing his history.