Can I deep fry in my Le Creuset dutch oven?
The enamel coating is put on by a high temperature process, much higher temp than the 300-400 F that you would deep fry in, so it will be safe to fry in.

The concern that this raises for me is the difficulty in cleaning if you fry repeatedly. After a few batches, there will be a film of oil that will form just above the level of the oil in the pot you are frying in. If you thoroughly clean it, it will not be a big deal, but left alone it will build up.

Also, deep frying in a heavy  pan is unnecessary, as you really want to get hte oil hot, and the extra thermal mass of the pan would just take extra heat. It is not bad to do so, but a thin aluminum pan works just as well for frying.