Verify a predicted protein in one genome in a different genome of the same species
This should be very easy to do. Here are some options:


Use a tool like Exonerate or GeneWise that can align protein sequences to genomic DNA while attempting to model splice sites etc. 
As you said, blast. There's nothing special in what you describe, really, this is what tBLASTn is for. Just use your protein as the query sequence and tBLASTn as the blast flavor which will take a protein query and match it against all 6 possible reading frames of a DNA database. Set up your assembly as the blast DB, and then blast as you would normally. 


Of the two, using the first approach is much better since it will try to build a valid gene model for you instead of simply finding the regions of high homology as blast will do. 

Finally, just for completeness, you can go old school and run a full de-novo gene prediction tool on your assembly. Something like GeneID for instance. But that's certainly overkill if you're just looking for a single gene.