Re: Untrained ukemi
There is an old video of O'Sensei using shihonage, I believe on a US marine. You should see the ukemi he tries to take.
IMHO, I believe when using Aikido on the 'untrained' your technique has to be very clear and strong, but not necessarily hard. Like working with a beginner in class but just a bit hard to produce your desired results. i.e. you may want to cause them some pain to give them a wake up call, but not an injury.
BTW, how long have you done Aikido and what style?