Can these be cut up safely?

I've used a grinder to cut several of them in two. I've had them smoke but never catch fire although I suppose they could. If they did, they'd just burn out the fuel oil. Depending on how much it might take awhile. If you're wanting to keep have something on hand to suppress a fire don't use water.

I drain all the oil I can, Then use Milwaukee Torch SawZall blades to cut in half.
Old towels / rags to clean out the sledge

If this is a conversion from Oil to Gas
Be sure to remove the fill tube from the wall, Both inside and outside BEFORE cutting and removing the tank as
Every year someone gets 200 plus gallons of heating oil delivered to their Basement / Cellar floor

A lot of towns have permits that have to be pulled so the work can be inspected and they are sure the tanks were disposed of properly

http://www.nbcnewyork.com/news/local...233534701.html << From 2013

http://nypost.com/2012/12/27/brookly...messy-mistake/ << From 2012

http://www.nbcwashington.com/news/lo...101417664.html << From 2010

There are Many MANY more
But you get the jest of it