In most cases, you can!
The HAKKO FX-100 Soldering Station uses high frequency induction to create heat using the same technology you find the the Metcal® MX Series Soldering Irons. These soldering stations use an induction system where the coil in the tip is set to work at a frequency of 13.56 MHz.
Some of these more popular Metcal® models are:
So, if the Metcal® power supply uses a standard F-Type connector (which most do), and the output frequency is 13.56 MHz, then you have the option to use the HAKKO FX-1001 Soldering Iron Handpiece and T31 Series Tips with your Metcal® power supply. On the other hand, you can also use Metcal MX series handpieces, including the MX-PTZ and MX-TALON tweezers, on the HAKKO FX-100 Soldering Station (Except the desoldering hand piece)
Think of it this way... if you have a music player that comes with a headset for listening to the music, but you prefer to use a different brand of headset for a better experience, then the choice is yours. There is no problem connecting your favorite headset provided it uses the right type of connector and it is made for the same purpose.
Metcal® is a registered trademark of OK International, Inc.