Relaxed shoulders are very important for correct technique,so too much lifting can affect this.
You might be able to produce anecdotal evidence that a specific routine result in someone who has difficulty in relaxing their shoulders, but I doubt that.
But even if that were true, it would not support your earlier assertion that heavy weightlifting is counter productive to aikido sensitivity. (And you still have not defined "heavy" nor "sensitivity"...I mean, is it safe for us to shovel snow or are we risking our aikido skills in doing so? How about helping push a car out of a ditch? Carrying groceries? Carrying a small child? Is it safe for me to pick up my mail?)
and they scare the s... out of me because I can not give them my body without worrying about serious injury and thats not a recipe for good Aikido.
Sounds like a trust issue, not a strength one. You might want to consider training elsewhere if trust is so lacking in your dojo or at the very least avoiding such partners. But again, that's anecdotal evidence that doesn't support your earlier statement.