Re Sigueiro, I would think the hotel is unlikely to be full - the question is more whether you want to stop there

As stated in other threads, there is supposed to be the possibility to stop in the sports hall, but I've never heard of anyone actually doing so - perhaps it's one of those where they only open up for prebooked groups. You are never far from the road on the Camino Ingles, and there's a frequent bus service Corunna-Santiago, so you could bus back to Ordes. There are several hotels along that stretch: as Johnnie says, at Meson do Vento, at Leira, there are several in Ordes itself (
Louro is the CSJ-recommended one (I've stopped there, nice family-run place with nice friendly prices

)), and at O Empalme 6km and Los Carballos 5km before Sigueiro.
Go to
http://www.turgalicia.es/caratulas/cara ... oxa&menu=4 and search for hotels/'boarding-houses' (i.e. hostals) in Ordes/Oroso municipalities. You will notice the one in Sigueiro isn't listed!
The route is indeed shady - archetypical Galicia, in fact. Apart from the entry into Santiago, which is rather tedious.