What is the estimator used in this paper for system identification?
Interesting paper!

Q1: yes, seems like OLS, non-blind. Usually OLS is non-blind. Some sort of regulated least squares can be used in a bayesian ML-setting, blind. This paper looks interesting: http://www.cs.berkeley.edu/~jordan/papers/lindsten-etal-sysid12.pdf

Q2: PBRS: https://en.wikipedia.org/wiki/Pseudorandom_binary_sequence. There is a lot of literature on this, e.g. Coleman Brosilow, Babu Joseph, "Techniques of Model-Based Control" 

Q3:they say it is semi-blind since the dynamics of the sequence generator is known.