Adding an Employer Sponsored Roth IRA to a B plan

Need some guidance please.  Had a client consult with an attorney who you know informed them of retirement plan options.  I'm sure they were all knowledgeable.  Yes I'm being sarcastic.  At any rate, they have approached me with adding a Roth IRA as a plan option so they can offer more to long term employees.  They have Roth in their B plan.  It's not a Safe Harbor B plan just as an FYI.  I know everything I can do with the B plan but I suspect they don't want everyone to benefit.  It's also an ERISA B plan.  Apparently they can put together an Employer sponsored Roth IRA and just contribute for who they choose, of course the contribution they make is taxable to the participant.  But how does this coordinate with the ERISA B plan?  Are there combined testing requirements since both Employer sponsored.  Can they do this free and clear???  I've never in 30 years had a client do something like this so insight on whys and such or other options, pros and cons of this, would be great?  Thank you.

What is a B plan?

Do you really mean "adding a Roth IRA as a plan option" or do you mean increasing the compensation of select employees and depositing the increment (or some portion of it) into an individual Roth IRA of each select employee?

B plan = 403 B

QDROphile I believe that’s what they mean increasing comp and contributing to a Roth IRA   Is there coordination needed with the 403b compliance wise?    Just haven’t seen this done before  

Isn’t offering Roth IRA as a plan option the same as depositing money in a Roth IRA for certain employees? This is why I’m confused. 

Before I go on a socio-political economic tear, does the emplyee have the option to receive the "contribution" in cash rther than deposit to IRA? 

Does this put you at ease relating to your part in it?

https://www.irs.gov/retirement-plans/ira-based-plans

It dos not help much with the practical design, execution, maintenance, and disclosure issues. It is also only the IRS position.  Other ERISA issues are implicated depending on the details.