Is it possible for Spectrum to listen for traps on multiple ports?
No, spectrum can only listen to a single port for traps.
Spectrum by default listens on port 162 but you can change that to another port by changing the following attribute in the .vnmrc
If you change the default port 162 to another port then you will need to restart the Spectroserver after modify the entry in the .vnmrc
Note: As a workaround solution you can consider to use a util such as trap exploder (or samplicator) on the Spectroserver machine to listen to traps on port xyz and then forward the traps to port 162 on the same box.
For example you might configure the trap exploder to listen on port 162 and Spectrum to listen on port 1162 (or some other port) then use the trap exploder with rules to decide which traps get forwarded to Spectrum.