One would assume that the legend that is Lazlow will return in Liberty City Stories. I certainly hope he does anyway. You should remember him from GTA3's Chatterbox radio station, plus his contributions on V-Rock in Vice City and once again lending his vocal talents for a short stint on WCTR on San Andreas.
Adriaan emailed Lazlow out of curiosity to see what he would say, he replied with this statement:
thanks for the email bro. i wish i could answer your question, but i've been given some free tshirts to keep quiet.
So Rockstar want him to keep quiet, not sure about you but I'm taking that answer as "Yes I will be in LCS but I can't tell you about it."
We'll keep you posted when we get an official word from someone.