Doug beat me to the solution on this one, this is where I was going with my questions about what functionality you needed. In a way, you're stealing an existing function in the system meant to do something else entirely, and repurposing here.
Just like a Project can have many Tasks underneath it, so can it have many Issues. The Issue functionality is designed for anyone on the project to file a report to the PM about things like 'rendering image in links' or 'software bug needs RAID' etc. Not a task, but a roadblock. In this model though, you're going to build a special custom form at the Issue level. Instead of asking normal Issue type questions like "How many hours will it take to fix?" or "Who are we throwing under the bus for this one?" you're going to simply ask for the link URL, and whether the link is active or not.
When your team want to add a link, they go to the Issue section of the project and hit New. Attach your form, and fill it out. That gets the data IN to Workfront, next trick is getting it back out.
You'll start with an absolutely standard Issue report. Column for 'Active', the URL and any other pertinent info (when was the link added, who added it etc) you want. Put that single report on a Dashboard. When you look at that Dashboard by itself, you'll see a summary of EVERY issue matching your filter (URL = yes, active = yes). Almost there, one more trick.
The next bit is one I wish Workfront documented better - when you take an object report (project/task/issue/risk etc) and you make it a dashboard displayed in a higher-order object then Workfront is smart enough to filter that report to only the related child objects.
Build a Project-level dashboard and display it in a Portfolio - then every time you switch portfolios it will only show you the information for projects in THAT portfolio. In your case, build an Issue-level dashboard displayed as a project-level tab. Every time you switch projects, it will reset the dashboard to only information on that project.
