Is it blkarray compatible with beamer?

You need a block environment within your blkarray environment, similar to the one given in Error with blkarray: Misplaced \noalign:

\documentclass{beamer}
\usepackage{blkarray}

\begin{document}
\begin{frame}{Title}

\[
\begin{blockarray}{cc}
A & B \\
\begin{block}{c[c]}
1 & 2 \\
\end{block}
\end{blockarray}
\]      
\end{frame} 
\end{document}

blkarray has two implementations a "quick" version for simple arrays and the full version if you want to do all the weird things that the package allows. For some reason eluding me at present beamer doesn't like the quick version so you can add to the document preamble after loading blkarray.

\makeatletter
\let\BA@quicktrue\BA@quickfalse
\makeatother

then it seems to work OK. Even the slow version is a lot quicker than the quick version was in 1992:-)