Hell ya. Turn lemons into lemonade. You could even pretend this was all on purpose. As the queue line reaches the end of the monster "exhibit" why not some bright caution light with loud speaker saying "Attention please! [something something something]. For your safety we are evacuating the exhibit. Please gather your items and proceed out the safety exit as marked by our staff. This is not a drill." And enter the scare part from there.
No reason your customers should feel like they got shafted by fire codes. Roll with it.
Personally, I feel like most big budget prop haunted houses I visited are nothing more than an monster exhibit anyway. They just don't know it.