Get accelerometer values from BNO055 using adafruit's Unified Sensor Library
Findings

If I use the same sensors_event_t in the code and use event.acceleration and event.orientation within the loop() and they provide me exactly the same values. I in fact get the same values for heading, pitch, roll and acceleration in x, y, z direction.

sensors_event_t event;
  bno.getEvent(&amp;event);

  Serial.print(F("Orientation: "));
  Serial.print((float)event.orientation.heading);
  Serial.print(F(" "));
  Serial.print((float)event.orientation.pitch);
  Serial.print(F(" "));
  Serial.print((float)event.orientation.roll);
  Serial.println(F(""));
 Serial.print((float)event.acceleration.x); // same as roll
 Serial.println(F(""));
 Serial.print((float)event.acceleration.y); // same as pitch
 Serial.println(F(""));
 Serial.print((float)event.acceleration.z); // same as heading
 Serial.println(F(""));


Sensor

I have a Blue Dot BNO055 sensor and it has marking on it for X, Y, Z directions as follows:


I crossed checked with the logic of Euler Angles from Wikipedia

If i rotate along the x Axis, I do in fact get roll (0 to 360) and so on. 

Inference

The Adafruit_Sensor library provides only orientation values when used with BNO055 and Linear acceleration values need to be called separately using the Adafruit_BNO055.

code for Linear Acceleration and orientation

  sensors_event_t event;
  bno.getEvent(&amp;event);

  Serial.print(F("Orientation: "));
  Serial.print((float)event.orientation.heading);
  Serial.print(F(" "));
  Serial.print((float)event.orientation.pitch);
  Serial.print(F(" "));
  Serial.print((float)event.orientation.roll);
  Serial.println(F(""));
//  Serial.print((float)event.acceleration.x); // same as roll
//  Serial.println(F(""));
//  Serial.print((float)event.acceleration.y); // same as pitch
//  Serial.println(F(""));
//  Serial.print((float)event.acceleration.z); // same as heading
//  Serial.println(F(""));

  imu::Vector&lt;3&gt; li_ac = bno.getVector(Adafruit_BNO055::VECTOR_ACCELEROMETER);
  Serial.print(F("Li. Acc.: "));
  Serial.print((float)li_ac.x());
  Serial.print(F(" "));

  Serial.print((float)li_ac.y());
  Serial.print(F(" "));

  Serial.print((float)li_ac.z());
  Serial.print(F(" "));
  Serial.println();

  delay(BNO055_SAMPLERATE_DELAY_MS);