You should be able to see what signal is coming from the player by looking at your display/TV info. It should specify what signal it is receiving, at least mine does. No, HDMI connection does not always presume a default 1080p signal.
If you find that the TV isn't receiving 1080p, you should be able to change that in the BD players setup menu. I would imagine that it's default setting is 1080p though since it's a blu-ray machine, maybe someone who has more first-hand experience with that player can confirm.