1) For example, select * from tab where c1 = 1 and sdo_anyinteract(...) = 'TRUE';
If "c1 = 1" is very selective, say only only one row or very few fows are returned,
sdo_anyinteract(...) may not go through the spatial index.
2) You can always use the /*+ full */ hint like:
select /*+ full(a) */ * from tab a where sdo_anyinteract(...) = 'TRUE';
3) SDO_GEOM.RELATE() seems to be what you are looking for.
Alternatively you can forbid only the spatial index and use your own index instead:
select /*+ NO_INDEX(a geom_spix) INDEX (a my_idx) */ a.* from tab a where sdo_anyinteract(...) = 'TRUE';