It is kind of important. If the provisioner gets knocked down, the supply line will be temporarily broken. Annoyingly, this can bug up provision lines quite a bit.
However, provisioners mostly (only?) get knocked down when you personally come across them in the wasteland and thereby spawn all kinds of nasties near them. If you are aware and go kill whatever is attacking the provisioner, they will get up again when the danger is gone.
Also, avoid assigning them to very long routes. Instead try to connect each settlement to the closest one, so you get a network of short routes. Having more than one route might also be wise for key settlements in dangerous areas, depending on how many settlers you can spare.
So it is a good idea to hand them some armor and decent weapons.
Using your own robot companions from the DLC as provisioners is perhaps a bit overkill, as they are extremely powerful but also costly. Unless you like building lots of robots :) You can also use companions, preferably those that you don't like and don't intend to take with you.