Maybe I'm being nit-picky, I wish we would stop using "poaching" to refer to the (legal) hiring of a person already employed at another company. Actual poaching is illegal, conversely anti-"poaching" pacts are collusive and illegal.
Source? According to Merriam-Webster, to poach means "to attract (as an employee or customer) away from a competitor". No indication of illegality here.
I'm not sure if you're saying you're not familiar with the meaning that the word has had since the early 15th century, but http://dictionary.reference.com/browse/poaching?s=t. It's application to business employment is obviously much more recent - I can't find a definitive citation, but I'd be surprised if this usage even dated back to the early 20th century.
I find it an inapt analogy to describe a transaction in a competitive job market.