From what I understand. No, you can not use your android to access the dark net. As there are imbedded applications within an android such as KNOX that are associated with the NSA, and now the NSA is associated with the FBI. There is certainly a way disable KNOX, but you cannot simply be so sure your phone is no longer tied with the NSA by one form or another. They call it Mission Impossible. Not only would you need to get a device unassociated with a cell phone service provider, but you would also need to DISMANTLE your device. If problems weren't enough with KNOX, there are articles that claim Orbot doesn't provide any anonymity That being said you probably won't make an attempt to harden your android. If you take privacy laws seriously, by all means go for it. There are numerous apps if you know how to use your android properly. One more thing you have to take into consideration is how you feel about your phone company knowing you're connected to TOR, I mean they know EVERYWHERE you go. There are however VPN applications provided for download through the play market, and even in some phones its part of the OS. The android platform is very tweakable, there should be some way to provide full anonymity, but as far as I know, and what I'm being told, you should not do it.
EDIT: I did not mention that KNOX is only implemented on Samsung devices. Thanks for catching that /u/k1ngm1nu5 .
you're stupid if you use any mobile device to fucking buy off the darknet