The boat I recently bought came with a gen1 hds5 in the console. I was just wondering if I was to buy a structure scan transducer and say an LSS1 box would I then have structurescan with this unit? Currently I only have sonar and gps. I know the picture would be small but that would be okay until I can upgrade units or add another large one and use h the hds5 for gps only. Thanks

Yes it is ...... but the screen will be small and not as easy to see.
If I might make a suggestion - save your money and buy a touchscreen unit (like a HDS 7 or 9)
it will have the structure scan module built in - then you can network your 2 units together and have many more options
As long as you don't want the structure scan 3D - Gen 2 and Gen 1 will play nice together

3D is only an option on Gen3