The Fed has two corporate facilities in-place right now: the Primary Market Corporate Credit Facility and the Secondary Market Corporate Credit Facility. ETF purchases fall under the SMCCF. Secondary corporate bond purchases are also under the SMCCF but they have not made any purchases yet. There is an issuer registration process that is thought to carry some stigma (Google "discount window stigma" if not familiar with something similar) especially with backlash towards larger companies taking advantage of PPP. There are no issuers currently registered.

As far as primary issuance goes, the same issuer registration process is in play. There are pretty punitive funding fees vs where syndicated bond issuance is right now so there's little incentive for issuers to participate in it as well.

Primary corporate markets are very wide open and have been ever since they announced these facilities. Investment grade issuance is at over $1trn on the year and have been very concentrated in the last few months. The Fed has bought around $6bn in ETFs so far which is really nothing in the grand scheme of things. The main effect these facilities have had so far is restore market confidence.