ok, im writing this song for my band, so far the last chorus is a solo with our bassist/singer singing over it. Is this a good idea? We only have 1 guitar.
why wouldnt it be a good idea,

the vocals act as a counter point, even though you only have one guitar, the bass still acts as dominant rhythm

the technique is quiet common is 80's
but still has cutting edge tecnique today
cant name songs, but i have heard Dream Evil, GnR, and well thats all i can think of atm hah
I've seen it done, especially with repetitive or simple sounding solos. Or like the singer comes in one or two measures before the solo ends or vice versa.
I hate my sig
If you try to make the singing harmonise with the guitar, it sounds bloody awesome - think the second solo in Welcome to the Jungle. Muse do it a lot too. Sounds great, if you can pull it off right.
Also, for a nice effect (Depends on the song ofcourse, doesnt always work out that well), you could try singing in unison with it. Just copy the solo with your voice. It cant be too intricate of a solo ofcourse. Sweeping vocals. Lol.