How are poles of Bessel filter related to cutoff frequency?
Yes - you can.
There are filter tables for all the well-known lowpass approximations - including the Thomson-Bessel response. These tables list the relavant pole parameters for the various filter orders.

For second order Bessel response the relevant parameters are 

$$Q_p=0.5773,\space \Omega_p=\frac{\omega_p}{\omega_0}=1.732$$

Explanation: The pole quality factor \$Q_p\$ is a measure for the angle \$\beta\$ between the pole position and the negative-real axis. We have \$Q_p=\frac12\cos\beta\$ . This angle can also be expressed using the given values for the real part (\$a\$) and the img. part (\$b\$) of the pole.

The normalized angular frequency \$\Omega_p=\frac{\omega_p}{\omega_0}\$ is the ratio of the actual angular pole frequency \$\omega_p\$ divided by the actual cut-off frequency \$\omega_0\$. The actual frequency \$\omega_p\$ is identical to the magnitude of the line which connects the origin and the pole position. This magnitude can also be expressed using the known values for \$a\$ and \$b\$. 

In this context, you should note that the above mentioned value \$\Omega_p=1.7320\$ is based on the following definition of cut-off: The cut-off angular frequency \$\omega_0\$ is defined as the inverse of the group delay, hence: \$\omega_0=\frac{1}{\tau}\$. 

This commonly used definition makes sense because - in most cases - the Bessel response is applied because of its time behaviour (delay filter). This is in contrast to other responses (Butterworth, Chebyshev, ...) where the frequency response matters primarily.

If the cut-off frequency \$\omega_0\$ is defined using the 3dB criterion for the magnitude the following normalized value applies: \$\Omega_p=\frac{\omega_p}{\omega_0}=1.2723\$.