According to the Social Welfare Rates of payment booklet (2006) if you are getting a reduced rate of Disability benefit, you can get an increase for your spouse or partner if their gross weekly income or earnings are €250 or less. At €250 you get €6.80 a week and then it goes up as your gross earnings goes down. So if spouse has for example €200.01 to €210.00 you would get €24.00 until you get , "up to €100 a week" is €71.30.
It says nothing about savings, but I would assume it might be the same as other benefits where you can have €20.000. between you and over that amount it goes down on a sliding scale. There is a government website called OASIS, if you search on AAM you will find a link as it's often mentioned here. So the answer to your question is yes, savings will be taken into account if it is over the above figure. But you would have to have quite a bit of savings to get interest of €250 a week.