If the above is true, the income will offset the debt in the DTI calculation, so who cares? 

But, if the deal is a true ABL play, I may not even look at a credit report at all.

I’ve done some research and have found that some banks will allow the seller finance portion from the seller to go towards the down payment of the loan, is that true?

Typically a few types of PMs out thereThe individual agent, little to no staffThe PM company that's a set it and forget it, glorified rent collectorThe PM company that's a true partnerI would on top of the suggestions abovesearch for a PM that owns their own portfolio tooThey treat your asset like they treat their own portfolio- There should be a full staff and readily available to answer the phone1.

Short and sweet here: There are no true DSCR HELOCs.

I personally think there is just not enough comps yet to show the true value of ADU's.

True.

Is that true? 

The tried and true version is pulling a list of properties whether you're targeting distressed homes or high equity homes in which case you can pull on something like Propstream or Propwire, you can skip trace through them or someone like Prime Tracers which has a pay as you go system. 

True, but (a) they were typically experienced investors, and (b) today's market includes record prices and high mortgage rates, which is a double whammy.