BiggerPockets

As long as you can disclose it to the other lender....yes.

If you are trying to get around disclosing it for some reason it is probably loan fraud. For certain loan types the lender will care and for others they won't.

The loan constants for credit cards are outrageous. You'd probably be better off seeking other financing.

If you do some Google searches there are actually pretty clever little games people play with zero percent balance transfers to put "free" money to work using credit cards. Learning to game the system and keep the plates spinning isn't really free to me, but there are many financial bloggers that go into excruciating detail about this sort of thing.

This money could presumably be used as equity in a loan as long as it was disclosed. Cash advances with cards would be subject to interest, but you can use those too.

You may consider finding a bank that will allow you to do a signature loan. Most banks cap these at $50k without sufficient collateral. That would get you pretty close to what you're looking to borrow; albeit at presumably higher rates than using conventional financing. If your project duration is short the hassle and transaction fee tradeoff may be worth it though.

I have done this once to help show better reserves (0 interest balance transfer check to my account). However, you have to be careful as you will then have a higher card balance. If you using conventional they may see this when they check the credit report one last time before closing. Be careful.

Putting the initial 20% on a credit card is a new one to me

Not sure how relevant this is, but I've used zero-percent credit card deals to finance materials, appliances, etc. for rentals in the past. It keeps my reserves healthy, but you have to make sure to pay it off before the retroactive interest kicks in.