I had one SEC 8 tenant last year get charged with possession of pot and lost her voucher as a result. 

In spite of this, once again YOU have the responsibility to accept or reject the premises prior to taking possession.

The LC was filed before the FC, the Trustee surely gave notice of the sale, if so, installment contacts are wiped out, treated as tenants in possession usually.

Once this occurs, you can usually get a Writ of Possession quickly so the Sheriff can go boot the tenant out.

Back when I had rentals, in TX almost ANYTHING the owner possessed was covered by state law to prevent the landlord from attaching it.

Other arrangements can also be worked out, such as in the event of default, you agree to continue making the payments and you could have the right of possession of the property, in other words, step into the borrower's shoes.

I don't want the possession of a credit card to be a filter in my tenant screening.  

Since the property is vacant and the judge awards me a judgement to take possession am I able to start the rehab process?

Until possession of the unit is returned to you, the original property condition report stands and can be used at end of tenancy for calculating the final return of the security deposit.Inspect the premises now and identify any damages that have already occurred and charge for them.

if you have filed a unlawful detainer I assume you don't have possession of the property.