i think i remember - a long time ago - there was a feature request to get the Eyes monitor feed as a GPU output, but that has not manifested.
it is possible to create a visual representation of the blob tracking system using Eyes++ and a lot of Limit Scale Value actors to process the outputs from Blob Decoders and control Shapes and Lines actors, maybe with a Threshold on the video feed if you want to simulate the blobs. The useful thing is that Shapes, Lines and Text Draw all have GPU inputs so you can daisychain them together to add graphics onto your video feed.
but maybe Isadora isn't the ideal solution to achieve this effect? object tracking in browsers is getting really good these days, i'm sure that a quick search around github will find an app that can do what you need instantly, then you can pull the results into Isadora with Screen Capture