The 30 % relief is relief on income tax. If you do not pay any income tax then there will be none to give relief on.
The gain is worked out separately from the relief.
You only need to report the EIS if you are claiming relief. You can see further guidance here:
Enterprise Investment Scheme – Income Tax relief (Self Assessment helpsheet HS341)
Capital Gains Tax and Enterprise Investment Scheme (Self Assessment helpsheet HS297)