I would advise against it, it can cast a halo effect against you. My personal advice is to have this person come with you and take you to the building (hopefully you can find your way from there). My sig other came along but hung out at the hotel/explored the city while I was being interviewed. You may come off as somewhat immature and dependent.
Open house and orientation are a whole 'nother thing, if someone is thinking that.
Two stories for you:
I got a chance to do ADCOM interviews last year, one student brought their significant other INTO the pharmacy office (literally the waiting area for students getting called into the smaller offices for interviews). Not only was that supremely awkward in itself, but this person was a) dressed in jeans and a dirty t-shirt and looked disheveled, b) was socially awkward as well. I helped give the tour after and they were holding hands...she was very well dressed and confident, and him being next to her completely ruined that image for me.
After everyone left I had a pow-wow with faculty/the other students and we all thought that to be very very strange as well. I don't recall the admissions outcome, and I don't believe the bf being there had any adverse result, but it's best not to chance it IMO.
Second story: a young person came in with one of their parents who didn't seem to be able to speak English. During the interview, you'd see the parent fixing the student's tie/clothing and the two of them bickering in their language. After the interview, one of the assistants looked up a phrase online and told it to the parent, who then replied, "OH! You do speak ______...you come over anytime, I make you dinner."
Hillarious. Admission result: accepted and currently attending (which is why I had to scrub all potentially identifying info).
Bottom line: don't chance it, and get a feel for the institution. We're a small school, so we really don't mind guests or other personal things...but I'm sure at certain schools, you wouldn't be able to get away with it. If you do go forward, your guest is an extension of you, make sure they're not socially awkward or dressed like they're going to fix a car.