Should I be concerned about a bumpy crusting rash on my vagina while pregnant?

Yes. This should be mentioned to the doctor at the next OB visit. It may be nothing concerning, but one possibility for a "bump" that forms a small blister that then has a crust is herpes. Other possibilities can be infected hair follicles or yeast. If it is herpes, it could change your delivery plan or require antiviral medications during pregnancy.