Yes, you can use the HOTTUB with other portable heaters as long as your hoses are compatible with 1/2" BSP, then you'll be able to plug right in.
Read more on how to set up your water heater with the HOTTUB here.
The quick-connect fittings on the HOTTUB are 1/2" BSP
These are the fittings that are included with the HOTTUB:
The blue fitting is for the water inlet and the red fitting is for the water outlet.
If you want to use your own fittings, you can unscrew the supplied fittings and plug in your own fittings.