Do I have to tell my LTD provider of I cash out some of my rrsp?

Not unless your policy requires you to tell them. Have a look at your policy. Generally LTD policies say that certain income is credited to the insurer (which reduces the LTD amount a person receives) but RRSPs are savings. That said, again, read your specific LTD policy to see if it requires you to disclose RRSPs taken out to the insurer.