Most developers compile the .lua source into byte codes using the "luac" compiler distributed with the SDK. That provides obscurity roughly comparable to compiling C or C++. There are tools that decompile Lua bytecodes, but they're not very good and their output isn't much more useful than you'd get from disassemblers applied to C or C++.
I believe Jeffrey Friedl compiles and then encrypts his plugins. Lua provides facilities for that that I think would be accessible when loading LR plugins, but I haven't done into how much of a song-and-dance that would require.