No, Nikon D3300 is not supported for tethering yet.
Here is the list of cameras supported : A list of cameras that can be tethered to Lightroom.
You said yet. Will it be? And are there any alternatives?
Tethering in LR uses the SDK from Nikon. It seems that the Nikon SDK does not support tethering for any camera model in the D3000 line.