Can I use an Antenna Splitter with my em-trak A100?

No, IMO regulations on the use of Class A AIS transceivers state that Class A units must be connected to their own VHF antenna and must not share a VHF antenna with other devices. This being the case, you must not use an antenna splitter to connect your A100 to an existing antenna system.

For help deciding which antenna is most suitable for you and advice what to do/what to avoid regarding installation, please search this support section for “What VHF antenna should I use?”