Ok i found the rule blocking access to connman. It was not, as stated above, in connman.conf but in connman-nmcompat.conf:
This should not be the problem, as the error says:
Error /net/connman/technology/wifi: Rejected send message, 3 matched rules; type="method_call", sender=":1.16" (uid=1000 pid=1027 comm="connmanctl ") interface="net.connman.Technology" member="Scan" error name="(unset)" requested_reply="0" destination="net.connman" (uid=0 pid=982 comm="connmand -n ")
As you can see, destination interface is "net.connman", but in the rule it blocks it is "org.freedesktop.NetworkManager". Still, in a fresh setup with only enlightenment, connman and chromium installed (no NetworkManager), changing this rule to 'allow' let's me use connman. I don't know if this is a bug in connman or in dbus.