It may be their right, but it's dishonest.
In the instance of offering a plugin to circumvent the EULA for Lr 6.x, yes, there is a level of dishonesty present. Paid, donation or free.
While I don't support the sale or purchase of Lr presets in general, I also do not think it is wrong for industrious individuals who took the time to create those presets to seek a monetary gain in offering those presets for sale.
Let's face it, for normal everyday Develop module presets, no one is holding Lr users hostage until they purchase presets. It's purely a merit based system. If the presets don't offer a value to the end user commensurate with the cost to acquire them ... they won't sell.
For myself, I much prefer to create my own and/or use the app as per the EULA I agreed to.