Hello,
The latest version 2.3.0 addresses this issue in the following way:
If a cart has been paid using cryptocurrencies with this plugin, then the vendor receives their commission in that same currency.
If the cart payment has been performed via any other gateway, then the amount transferred from the admin to the vendor is denominated in a currency that the admin has chosen to be a site-wide default. The conversion is done with the exchange rate that is valid at the date of the commission payment.
If the admin has not yet selected a site-wide default currency for commission payouts, then they will see a warning about this.
Regarding your other question, if you want to specify directly an exchange rate between the shop’s woocommerce currency and some custom points, use the existing code example to do so: https://gist.github.com/alex-georgiou/492196184f206002c864225180ca8fbb
with regards