Can a SWAT team member use whatever gun he wants?

It will depend on what department your with. Most departments with standing (full time) SWAT teams they issue your firearms and you use what is issued. Smaller department my have some leeway with what handgun you can use. When it gets to long arms most want all officers using one firearm. This is done for training reasons, ammunition capability and interchangeable magazines, the armorer will only have to attend one school, and finally interchangeable parts.