Determining the correct power rating of a braking resistor
To answer the question you asked, yes.

I just sized a few Brake resistors so while the information is fresh:

When a servo motor or any motor is slowing down a mechanical load, it is in essence transferring mechanical energy to heat and electrical energy.  The added electrical energy can be seen by a rise in the DC bus voltage of the VFD (your servo motor driver).  Often the amount of energy that would need to be stored in the DC bus raises the bus voltage to too high a level.  To prevent damage most drives can be equipped with an external resistor to "bleed off" the excess energy.

Like any resistor the two most important parameters are resistance and rated power.  The needed rated power is dependent on the application of course.  A good start point is match the resistor rated power to the rated power of the motor your VFD is driving.

The resistance needed falls under a range and is dependent on your VFD and the DC voltage your VFD nominally runs at.  The upper resistance limit is determined by your DC bus voltage.  The resistance needs to be low enough that when the DC bus voltage is applied to it the needed power is consumed by the resistor.

Upper Resistance Limit:

\begin{equation}
R_b = \frac{V^2}{P}
\end{equation}

\begin{equation}
Where\ R_b\ is\ the\ brake\ resistance,\ and\ P\ is\ the\ desired\ power.
\end{equation}

The lower resistance limit is dependent on your VFD and should be in its datasheet.  If the resistance is too low the current pushed through the brake resistor will burn out the VFD's brake driving circuit.

As long as the resistance is within this range you should be ok.  Typically the VFD simply fires the Brake Resistor circuit when the DC bus voltage reaches some threshold, and turns it off when the DC voltage drops again.