I'm not sure, but I think it won't quite affect their budget allocated for the signature campaign as they're allocating Btc. Though they might spend more fractions of Btc compared when Btc is in a higher price, but the same goes when someone uses their platform and deposit their crypto.

The huge difference would be for the budget allocated to run the business long term and the willingness for the owner to risk more budget to promote the website.
You won't expect to get good result with a limited capital in a market where competitions are air tight. Most gambling websites offers common and unique bonuses and rewards to attract more users.

If the sig campaign won't work for them, then for sure the problem would be on how they run their promotions. That means, it is less attractive offer than the other online casinos.