They are slightly different.
'Is ....OK for you?' means 'Is this suitable/convenient for you?'
This is likely to be about a fact.
'Is ....OK with you?' means 'Do you have any objections to this?'
This is likely to be about an opinion.
For example, if you are planning a dinner party, and you know that a guest has allergies and isn't able to eat certain foods, you would need to ask if a dish is suitable, so you would say 'Is this OK for you?' . You wouldn't say 'Is this OK with you?' in this situation, because this is about a fact, not an opinion.
'That's OK with me' - or even 'I'm OK with that' - means 'I don't mind'.