@Dennis Tierney is correct you're going to find it difficult to get financing for this from a traditional bank but there are other lenders you can find. 

I currently own two properties, one of which is my primary residence, and the other barely breaking even.

It's a great option for 1st time homebuyers, but remember that it's typical for the condition of the loan to be that you must live in the home as your primary residence for 1 year or more in order to qualify!

Loan type is traditional.

my co-worker is from Canada and was working in the US for over 3 years on a visa before buying his condo. he had no debt and had strong salary history - however, he couldn't qualify for a traditional mortgage because he didn't have any credit history in the states.

Are you looking to do a traditional buy and hold?

It's been my understanding from the research/coursework I've done that this is almost certainly against their primary mortgage's terms.How common is it for banks to call loans in these situations & how safe is it for people to offer seller-financing in these situations?

For retail many ground leases are 20 year primary term or lower with options thereafter.

so I just got my HELOC secured here in Austin on my primary home through BBT. 

Hello, I'm interested in a property for my Primary that will need work and I've started the process for a 203 loan.