Can I use stall detection as my only obstacle detection or will that damage the DC motors over time?
Motors work the same way as other electronics.  (You need the smoke to come out before it stops working.)

Seriously, if you do not allow the overcurrent to heat up the motors, they will be fine.  \$I^2 t\$ is what kills most things.  Do not exceed that as specified by the datasheet.

For a small motor the thermal constant might be say 10 minutes or 600 s.  Derate the full load to 99 % and assume the bump current is 500 %. This means that you have $${600 - 99\% \cdot 600\over 25} = 240~ms.$$

This means that you can bump into things a total of 240 ms of time in 10 minutes.  This can be achieved by switching off the motor very quickly or derating the full load a bit more.