i agree with DharmaDefender who said that people who are into illegal stuff are rather unlikely to be attracted to the three principal paths. However if Dorje Shugden can grant them some worldly wishes, it may provide the incentive for them to propitiate Dorje Shugden and that would be how Dorje Shugden hooks them in to the Dharma which he protects.
I always think that it's better for everyone to have some benefit than none at all. These people who are into illegal stuff are the ones who really need the blessings of Dorje Shugden to turn their lives around, so why would the practice not be appropriate for them? If the practice is for holy people only, 99% of the planet would be excluded.
Dorje Shugden is manifested particulary for this degenerated age where greed, anger and desire prevail every single mind of the deluded sentient being. So it is most appropriate to introduce Dorje Shugen to people who are doing illegal traits, same reasoning with what WisdomBeing has mentioned above.
At the age, how many of us go to temple to pray for enlightenment?? And how many of us go to temple to pray for more money? Dorje Shugden can sepcifically target our greedy minds by fulfilling our wishes and then in turn when we make the connection with him, we are allowing a chanel for further dharma to be taught.
There are 5 forms of Dorje Shugden, for people who are in illegal business, perhaps introducing them
"Karma Shugden"would be great as they are completely deluded and are loaded with heavy negative energies.
Five families (aggregates)
Duldzin Dorje Shugden: consciousness. He gives wisdom and shows the way.
Vairochana Shugden: form. He purifies negative karma and obstacles.
Ratna Shugden: feeling. He increases what is good.
Padma Shugden: discrimination. He brings peace of mind.
Karma Shugden: compositional factors. He helps in overcoming delusions and harmful energies