depends.
If you have info on a traffic warrant, yea probably not going to rush right out and pick that up. But if you have info on the where abouts for a criminal warrant it may be followed up. Anonymous remains that way if it is reported correctly... aka if you call 911 from your cell phone they will have your number. However, if you call from a public phone aka a pay phone, to the actual police department that will be involved then yes, you can remain anonymous if you so please.
It may not remain anonymous if you provide information that is later necessary to prosecute, but if is just a warrant you should be fine.