Are they in the courtroom with the accuser?

Yes, frequently.

I have read a study the it influences people into seeing that person as a victim.

I'll update this when I get a response from my Dad, but my understanding is that the defense can object if they don't want it. Success would probably depend on the court room.

Edit: I got this wrong. He won't do it in a jury trial. They don't want to take a chance on losing it at appeal. Preliminary exams and bench trials in both circuit and family court.

All that said(my opinion begins here), I don't see how the young child testifying at the sexual assault case could be seen as anything other than the victim in the first place.

One of the major problems with juvenile assault cases are that it's really easy for the accused to intimidate the child in the court room, even using simple things like direct eye contact. There's already allowances made for children because of this(like 1 way screens so the accused can "confront" his accuser, but the accuser can't see him). I don't see a dog as any different than that.

....But yes, this question was me answering. I'll get ahold of my Dad shortly and update this with his answer.