Is it okay to go through a nissen fundoplication for GERD after having a gall bladder removal done on me?

Yes. Yes. Once you have recovered from your gallbladder removal there is no reason why you can't have a fundoplication for reflux if your doctor feels a fundoplication is a good treatment for your reflux.
Yes. There are some risks in that previous surgery can let to scar tissue formation and this can make the fundoplication surgery more difficult for the surgeon especially if he will try to perform the surgery laproscopically. There are good criteria to determine if the fundoplication is necessary.