I'm sure many of you know the staff 'Sanguine's Rose', which summons a Dremora to fight for you.

Is the Dremora that the staff summons weaker then the Dremora Lord which is a Conjuration spell or are they both the same thing?

Yeah the Rose spawns a weaker version, but it's still pretty tough.

It is roughly on par with a Draugr Wight and a half, or a Scourge (slightly weaker, though it can beat a scourge alone if it fights effectively)
The Dremora Lord can take on a Deathlord then another (though not at the same time in most cases)