1. Solaris, AIX, HP-Unix use Unix kernel. Then how Unix developed in Bell labs become proprietary ?
It is proprietary because--
a) Bell Labs was a proprietary firm belonged to AT&T;
b) It was copyrighted under the Federal Laws;
c) And was sold to another proprietor company under the terms of Copyright Laws. It shall not become a free software until the owner company changes its license into Gnu/GPL (as CopyLeft) freeing its source code from the burden of copyright laws.
2. On what basis GNU/Linux is treated as Unix-like OS, although it uses Linux Kernel.
GNU/Linux is Unix-like because Linux, as a kernel, was/is implemented according to unix philosophy and seeks to run like a clone of Unix; and indeed it is running like (or better than) Unix today. A clone is not the original, it is merely a clone, the source code was written afresh, it did not use the source code of Unix thus Linus Trovald did not infringe the copyright protection extended by the Federal Law to the unix source code.
Hope this helps.