I sure hope I'm putting this in the right place!

Okay basically, my mom had this low life boyfriend, who we believe stole jewelry from us. She knows he has a safe in this room where he works, and she thinks he's got our things in it. If she were to go to the police and tell them this, would they be able to go there and ask him to open it, or do they need a search warrant? Thanks!

I'm not an expert on this, but I believe that the police must have a search warrant unless the low-life consents to the search. He would have every right to refuse unless the police had probable cause to do so, for example, he gave them permission to enter the office and they happened to see the jewelry in plain view outside of the safe, or they had the legal search warrant given them based on showing probable cause to a judge. Or perhaps if he were arrested at the office on an unrelated crime or warrant. Unless you have more evidence that he is the culprit, it's best to chalk this one up in the loss column and hope that mom dumps this guy pretty quick.

The police would need a warrant and without more than yours and your mother's suspicion to base it on, it is unlikely that a judge would issue a warrant....HOWEVER: If the safe belongs to the employer, rather than to the "low life boyfriend" it is possible that the employer might consent to a search, in which case no warrant would be required.
Unless the missing jewelry is of great value, monetary or sentimental, I agree with with Gerry about chalking it up and simply losing the loser.

Regardless of the value. If you think the guy stole your moms stuff. You better try to get it back. It's not the value behind it. It's the principle. I'm not saying break the law. Although before that is what I would sugest.
I recomend doing it the right way. Get his bosses permission to enter the safe, or get the police involved.