In orac there’s a module called notegen under the sequence section.
If you put that in A1 then have your synth or sample in A2. If you go go to A1 you can start programming what specific notes you want and the probability by going through the multiple pages. Note it starts automatically when speed is more than 0ms
*Although Ive noticed theres no way of getting the C to be 0. its alwas got a minimum probability of 50 which can be edited in Pd. Will try my hand at it.
There are other ways to simulate randomised arps by using the sequence module in A1, record your synth/sample loop, A2 have your synth/sample and A3 can be a slicer (which is a little tricky at first but you get the hang of what each parameter does after a while).
Would be cool to have a stand alone probability module that could control your arp/sequence but for now these seem to get intereting sounds.
Cant speak for the sq1 but the organelle can do a lot with tinkering and forum diving