BCRider

Nope, technically it won't work. The difference in mineral oil and DOT fluid systems is the rubber seals in the caliper and lever. DOT fluid has seal swelling agents in it where mineral oil requires the seals to be the right size to start with so they are a hair tighter fitting and could well be a different rubber. Using DOT fluid in the XT lever may well cause the seals to swell and that'll make the lever stiff and possibly slow or stop it from returning.

Now you may think "GREAT! I'll just use mineral oil then!" Nope, if you do the seals in the caliper will eventually shrink back in the absence of the DOT seal swellling agents and at that point you could easily find mineral oil seeping out of the piston seals and onto the pads and disc.

So you need to use the parts with the oil or fluid they were designed for unless you're willing to risk a leak or a jam. Now with the small sizes we use in our systems it is possible that you CAN get away with a good clean and rebuild and then run either fluid option and not have any trouble. But there is a gamble involved and if it doesn't work then you'll be shopping for a new lever anyway.

You're best off getting a Hayes lever since you know it'll match the requirements for the caliper and that it is DOT fluid compatible. And it doesn't need to be THAT lever. A Mag or HFX will work interchangably since they are both intended to be used with the regular Hayes two piston caliper.

The hose is no problem. Any good LBS that services a lot of off road bikes these days will have bulk hose and the odd olive hose ferrules that Hayes uses in stock.

Also unless the lever is busted you know that there's rebuild kits available?

If you're not worried about hurting the XT lever you can try flushing it first to clean out the mineral oil and then fill it with some DOT fluid. Let it sit and try it daily for around a week to 10 days. By that time it'll be as tight as it's going to be if it is going to tighten up at all. If it's still good and snappy then you win the Brave Brake Lotto and can safely go ahead and fit the parts together. If the lever gets stiff and sticky then you lost and you'll want to strip it and get new seals to prep it for going back to mineral oil. As for trying the caliper on mineral oil I wouldn't bother. A sticky lever is one thing. Oil on your pads and disc is a whole other step in a bad direction. The problem is that it likely won't leak until you're stopping hard. A few of those and then you won't be stopping....