I think your initial sentence: "I would like to know on recommendation to use VSX at aggregation layer between Core & Distribution." caused a little bit of confusion and the answers you've read.
You should have written: "I would like to know on recommendation to use VSX at aggregation layer and at Core/Distribution layers." ...not between them.
By the way...VSX technology, despite being young, is rock solid and mature (especially if you start with ArubaOS-CX 10.4 software branch and you follow the best practices/guidelines in your deployments)...no matter if you're going to implement it at Core, Distribution or at Access layer (at a pure Access layer it's a little bit wasted and indeed Aruba suggest to use VSF as virtualization technology either on ArubaOS-CX based Switch series - I'm referring to Aruba CX 6300 - or, eventually, on older ArubaOS-Switch based Switch series supporting VSF such as Aruba 5400R zl2 with v3 zl2 Modules or Aruba 2930F).