How to dpm() an object value? If I run dpm($form); I get an array containing objets. Now I need to just dpm() the uid of the node object. 

How do I do dpm() to isolate an object value?

I tried with dpm($form['#node']['uid']); but not working.

Please look the capture to make my question clear:
You would use:

dpm($form['#node']-&gt;uid);


As you rightly say the #node variable is an object, and object properties in PHP are accessed using the -&gt; operator. 

Have a peek at the PHP Objects documentation for a few more details.