If by "safety school" you mean that you'll almost surely be accepted to the grad program... I think the answer is "no". Even if you've done reasonably well as an undergrad, for grad admissions you are suddenly competing with people from all around the world. The "playing field" is suddenly much different.
Yes, some universities do try to take good care of their own grads, but this is very inconsistent from place to place, and depends enormously on the current administrative cadre at a given place.
Also, typically R1 universities graduate many more undergrad math majors each year than they have openings for (funded!!!) grad students. So the numbers/money game alone restricts what your home place can do.
So, in summary, if you are one of the better math majors in your year, it would be sensible to apply your own place as a back-up. But/and you might want to make it clear to your own dept what you are doing, since many depts will simply not make an offer to prospective students who give every indication that they wish to go elsewhere... since the current rules/guidelines for grad admissions in the U.S. effectively punish programs for making offers to students who won't accept.
Talk to your faculty at your place about the advisability of this...