I'm not sure if this is a double typo of if you do not understand
about the agreement you are asking about. It's called "play-or-pay".
This agreement means you will pay the actor to block out a specific
time period in their schedule. If you do not make the film during
that time frame the actor keeps the money. So yes, you would
have to prove you had the funds. In most cases you would need to
pay the actor the entire amount, up front.
I can see why people would do it. The "right" actor can have such a huge impact on the ability to get financing there are situations where I'm sure it's the best route open to the producers.
Some producer do it. But not to use the actor to get financing.
Here's the problem. If you offer a pay or play deal you are
obligated to pay them if you do not make the movie. What
happens if you do not have the money now and then cannot
get the financing? You must pay the actor the full fee.
What you are looking for is a Letter of Intent. The actor agrees
to be in in your movie but is not paid until you have raised the
financing.