In short: Yes, you can! But you should always bear in mind that especially the low bass range of a subwoofer benefits from the DSP filters set with GLM. This significantly increases the precision and linearity of the bass range.

This is what you need to know if you want to use a non-SAM subwoofer: The subwoofer must provide a high-pass-filtered signal for the speakers or you will have to set the matching low-cut filter on your SAM monitors using GLM.

These subwoofers have the 85 Hz crossover and provide a high-pass filtered signal (no low-cut on the speaker is needed):

7040A, 7050C, 7060A, 7060B, 7070A, 7071A

If a subwoofer is sending a full-range signal, then please follow the steps described here:
https://support.genelec.com/hc/en-us/articles/29843134315282-How-can-I-activate-the-low-cut-filter-of-Genelec-SAM-monitors

You should then adjust the subwoofer's frequency response with the DIP-switches. Here you can see how to do it precisely with a free software like Room EQ Wizard:

Next step: Please measure and optimise your SAM speakers with GLM.  

You will now have to adjust the level balance and the phase. Here you can see how to do it:

If you don't have access to a measuring system like REW, use a standard 85 Hz test signal (https://www.genelec.com/audio-test-signals) and do it by ear as described in the manual of your subwoofer.

Finally, connect your source to the subwoofer inputs, and the outputs of the sub to your speakers.

Enjoy your system!