This really depends on the nature of the industry you are in and the level of loyalty your competitors inspire.

For dentists and other services with immediate need, I find bidding on competitors brands to be very effective.

For industries with minimal demand, like emerging industries is practically a best practice to do this.

The simple reality is that using a broad match keyword will likely surface you on a competitors brand search, so I dont see how it is even remotely frowned upon. Your competitors might not like it, but its very unlikely they'll even notice it.

You should even feel free to use their brand in your copy as long as its not trademarked. Some people use Dynamic keyword insertion to do this.