While JIRA itself isn't open source it does have open source license... The only issue that I can think of right now is if you want to use it within a company that doesn't do open source (i.e. can't comply with the open source licensing of Atlassian).
What did You have in mind: What tracker is used in Seam development cycle? Or any issue tracker developed using Seam as dev. technology?
I don't know any particular issue tracking system have been developed using Seam so far.