Can I give dyna gro bloom in veg ?

is this a bad idea?

Not really, you will not be giving them enough N and too much P, unless you have amendments in the soil (say you used blood meal and you need to give them a little P and K).

If you can't find any DG Grow, you can use fish oil to supplement the veg stage (5-1-1 or 5-3-3).