BLDC Motor Constants: Why is my Kt and Ke different?
Please keep in mind how each are defined

\$K_e\$ is defined as the PEAK line voltage per mechanical rotor velocity with a fundamental equation \$K_e = \frac{V_{pk,ll}}{\omega_m}\$ 

\$K_t\$ is defined as the PEAK torque per phase current with a fundamental equation \$K_t = \frac{T}{A}\$  

The units of \$K_e = \frac{V \cdot s}{rad} = V\cdot s\$ (since radians are unitless

The units of \$K_t = \frac{N\cdot m}{A} = \frac{J}{\frac{C}{s}} 
 = \frac{J\cdot s}{C} = V\cdot s \$

\$K_e\$ and \$K_t\$ have exactly the same units and in the ideal case ( no mechanical drag, no magnetic saturation) they are comparable. I say comparable not equal because there is the \$\sqrt{3}\$ factor due to one being line-line and the other being phase.

In practice... \$K_t\$ is defined at rated current and as such there is magnetic saturation resulting in \$ K_t &lt; \sqrt(3) \cdot K_e \$ (how "less than" depends on saturation)

From your comment 


  The spec values on the Excel sheet are what I am confused about. The
  Kt is 0.55 N-m/Arms and the Ke is 0.318 Vrms/rad/s. I was under the
  impression that the numerical value for both would be the same, given
  that they are expressed in SI units.


\$ K_t &lt; \sqrt(3) \cdot K_e \$
0.55 &lt; \$\sqrt{3} \cdot\$  0.318
0.55 &lt; 0.5508

Thus your electrical machine datasheet is in alignment