postie357,
May I suggest:
Don't be too quick to get a new cam cover gasket.... Gasket usually stays intact on the cover....I have re-used mine (many bikes) many times IF not broken...
Welcome!
No, you do not have to drain the oil. A little will probably come out when you pull the cover, so make sure you have a oil pan underneath just to catch the 1/4 to 1/2 quart that may come out. You will need to remove the exhaust as well.
As much as I hate to disagree with Bubbie, since he knows a lot more about bikes than I do, for the $6 or $7 that the gasket costs, I'd go ahead and just replace it. But that's just me. I'd hate to get it back together only to find a leak and have to do it all again.
If your just checking the tensioners I suggest leaving the bike on the jiffy stand and not vertical on the lift. This will let the oil stay to the inside of the chest. I also snake a garbage bag between the bottom of the cover and over the frame for any spillage. Another trick I use when changing the oil filter is loosen it till it just starts to hand spin. I then cover it and the filter housing with a one gallon ziplock bag. I use the outside of the bag to slowly spin the filter off an let it drop inside the bag. Absolutely no mess on my frame.