I didn't know that Shimano made 105 flat bar shifters and brake levers. Interesting.
Shimano road 11 speed groupsets use the same shift cable pull increment and derailleur actuation ratio, so the SL-RS700 shifters will work with Ultegra derailleurs.
The BL-R550 brake levers are obviously made to work with road caliper brakes. (Different brake systems have different cable pull and caliper leverage ratios. A set of levers for V-brakes for instance would not work with road calipers.)
One thing to be aware of is that replacing drop bars with flat bars is going to significantly reduce the reach geometry. If that is one of your goals that's fine, but if you have a good position when on the hoods of the drop bars your will probably find the flat bars cramped. You may need a long stem to get a good position.
frames for drop bars are generally have a shorter reach measured to the head tube than frames for flat bars. This is because drop bars add more reach than flat bars.