This is a good question. There are many judges in the book of Judges and some of them are not spoken of all that much. So, it is hard to tell where their religious commitments were. In addition, the book of Judges is such a dark period for the Israelites, the worship of other gods was common and all over the place. So, it is reasonable to assume that some of the judges were not completely faithful to God.
With that said, generally speaking they did not worship other gods. Not to worship god faithfully is different than serving other gods. There is an nuance. This is why they were judges. They were established by God to bring the Israelites back to himself. So, while they were far from perfect - all you need is to think of Samson - they were not idolators. They were God's appointed leaders for the time to bring Israel's heart back to himself. Here are a list of the judges:
Shamgar 3:31, Tola 10:1-2, Jair 10:3-5, Ibzan 12:8-10, Elon 12:11-12, Abdon 12:13-15, Othniel 3:7-11, Ehud 3:12-30, Deborah 4:1-5:31, Jephthah 11:1-12:7, Gideon 6:11-8:35, Samson 13:1-16:31.