I want to preface my comments by saying that I don't have arthritis nor do I have a pacemaker but I will add some information here that may help you as a long time user of the tunze osmolator and a medical student myself:
For starters once you place the ATO magnet down in your sump etc, you should not have to adjust the magnet much, if at all. You should be able to just "snap" (unhook) the auto sensor and float switch for general cleaning purposes without ever physically removing the magnet. I clean mine every few months in vinegar to ensure no calcium build up interferes with ATO sensing. Also the magnet themselves, while very strong for a magnet (compared to things like fridge magnets) are still not very hard to remove (again depends on severity of your arthritis, but they are not as bad as the warnings make them seem). Just make sure to keep the magnet separate when installing and keep them on each side of the sump glass respectively (they are hard to remove if stuck directly together, but I find them relatively easier to remove if the sump glass is kept in-between them, separating both halves)
As far as a pace maker, I would recommend you TALK TO YOUR HUSBANDS DOCTOR, as he will know the specifics of your husbands pace maker model, and general operational guidelines..... however I would say that most recommendations I have seen state that keeping magnets 8-12 inches away from the pacemaker should prevent any possible interferences. Again I want to state PLEASE ASK YOUR DOCTOR, however my recommendation is just from what i have come across as a medical student and would think that he should have no issues being around it, just want to always hold the magnet out, and away from his body as far as possible for general precaution.
So overall I feel you would want to use the magnets as it would be the "safest" way to ensure the ATO stays in place, just make sure to call your doctor and explain the situation and get his personal advice, but i believe at 6-8 inches you should have no worries as far as magnetic field interference with the pacer itself. Please let us know what he says, as I for one am interested in his recommendation.