I think it would be unusual for a mandolin to need an amp in order to be heard, even amongst a throng of squeezeboxes. The sound is at a higher pitch and usually cuts through.

Whether you can hear yourself is another matter. The sound projects away from you so in a noisy environment it can be difficult to hear yourself (even concertinas can have this problem). You might just get away with it if it is used solely as a foldback monitor (although your immediate neighbours may not be be very happy) but generally amps are unwelcome at sessions unless used for entirely electronic instruments (eg keyboards and basses) and turned down to match acoustic levels.