Here's the situation:

I'm looking to book a hotel for a vacation 12 months away. The stay has a $1,500 refundable damage deposit, due in full at the time of booking.

Can this refundable deposit count towards the minimum spending requirements for sign up bonuses?

The better question is, Why wouldn't it? The CC issuer doesn't know it's refundable. What's the difference between that and any other purchase from any other retailer that allows refunds?

The key would be whether or not you actually get that refund, and when.

However, if and this is the big if, the refund is credited back to your original credit card, then those award points will usually be taken back by the CC company. This usually occurs because the amount refunded is subtracted from the new balance you owe, and the points awarded are then calculated on the net amount left on the CC bill. .
That being said, if your original charge was during a bonus month (for example 5x bonus for hotels), and the refund is out of the bonus period, then you may benefit from only the base being refunded, not the bonus.

Not always the case. I have had refunds go both ways as far as points were concerned.

It is possible they could claw back the points from the signup bonus. If the refund is a year later though, I doubt they would do that.

I tend to agree, if the refund happens a year or very close to a year after the charge to meet the spend threshold, the bonus is safe. Else there is no telling giving what AMEX RAT has done since last year and now specific languages are incorporated in ALL AMEX cards, including the claw back if a refund is made on charges to meet threshold.

Personally I would NOT put anything that has the slightest possibility of return, within the period to meet spend requirement for a sign up bonus so NOT to give AMEX system any chance to initiate a crawl back, even though you subsequently meet the spend still within the period with other charges. Too many horror stores around the net that people who have very legitimate returns such as merchants not fulfilling orders, goods shipped being defective etc, have to battle with AMEX on their crawled back bonuses.

it is a new environment and one should proceed accordingly.

This is not directly related to Manufactured Spending, and is therefore being moved to the general Credit Card Programs forum.