There is no general way to verify if an unspecific app has been torifyed, but you could simulate behavior of https://check.torproject.org/ web service (which essentially looks up HTTP client address in tor exit node list and reports if found or not) using general purpose utilities as follows:
Launch terminal and telnet to public route server
user@android:/ $ telnet route-views.optus.net.au
At server prompt issue
show users command
Line User Host(s) Idle Location
2 vty 0 idle 00:01:32 126.96.36.199
* 3 vty 1 idle 00:00:00 tor-exit01.baconsvin.org
4 vty 2 idle 00:04:46 188.8.131.52
5 vty 3 idle 00:00:46 cg.eastlink.ca
Interface User Mode Idle Peer Address
* at line
vty1) denotes an active line you are using to connect, and location of your line's endpoint (
tor-exit01.baconsvin.org in this case) clearly marks tor exit node (some exit nodes do not have so friendly reverse DNS, so check against known endpoints like your ISP, VPN or look up in tor exit node list).
Thus, you just connected through tor (try the same with tor stopped to see the difference) and hence, Orbot's transparent proxying feature works for all apps.