preexisting conditions and group insurance?!

I had a job with health insurance but lost it because of a work injury. The workmans comp is making it go through court to pay me so I have no income right now. My wife has a preexisting medical problem. I went onto COBRA insurance but it went over 100 percent in January and I could no longer afford to make payments on it. About March 5 I will go over the 63 day that I have to replace my insurance.
I have found another job with insurance but it requires a back ground check that may take me over the 63 day time limit where they have to take preexisting conditions.
What I need to know is if it is group insurance, do they cover preexisting conditions or will I end up losing coverage on her?
If they do not cover preexisting conditions can I get insurance for a short time to cover that time? An insurance salesperson told me that short term insurance will probably hurt me instead of help me. That I don't understand because I have to keep insurance to keep her covered.
Where do I go to get absolute rules pertaining to this?
Any guidance will be greatly appreciated