Your tropical region is probably just fine for your Pearlscales.
Goldfish are not coldwater wish, but temperate fish, meaning they can withstand large differences in temperature depending on the time of the year (freezing temps to as high as 85 degrees).
Because Pearlscales are a double tailed goldfish, it means they are a little more sensitive to temperature and prefer the water to be between 70 degrees and 80 degrees. Koimaiden mentioned she actually has a heater for her fancy (double tailed) goldfish because she lives in a cooler climate.
The Pearlscale's temperature preference does NOT mean they can live with your betta fish, however. Pretty much everyone here as given you the reasons why. More importantly, they need a bigger tank.
I just rescued two, single tailed (comet) goldfish recently and learned I needed a 55 gallon tank to keep them both happy! Goldfish need LOTS of space to be happy and healthy, especially since they produce so much waste. They also need filters.
Any pictures of your pearlscales? I want one so bad, but they'll have to wait until I'm moved out and can get another huge tank :)
If you want some really good info on goldfish (and bettas), check out this blog, written by one of our members, thekoimaiden - she is great with goldfish and has taught me everything I know over the past few months!