What is the reason for doing a nested repeat region? I don't think you can add proper BOM balloons for that, but if you instead use a recursive repeat region, there are no problems with adding BOM balloons. Just use a regular BOM and go to Repeat Region -> Attributes -> Recursive. If you want to limit it to three levels, you can do that with Filters. If you want it indented, you can do that with Relations. The only reason I can see for nesting is if you want different columns for your lower-level items (but perhaps there are other reasons).
