As long as your layover is less than 24 hours and it’s all on the same ticket, then yes they should be able to check your bags all the way to Thailand. They will transfer your bags in Siingapore for you so you won’t need to worry about them. Just make sure at check in that the bag is tagged all the way to HKT. It doesn’t matter for immigration in Singapore for your bags, whether you’re staying airside for transit or entering the country during your layover. Enjoy your trip!