Are there any non-pathogenic gram-positive bacteria in human gut?
A recent Nature article, entitled A new genomic blueprint of the human gut microbiota, contains the following Figure:

 

[Fig. 3 Phylogeny of reference and uncultured human gut bacterial genomes]

I don’t know much about bacteria, but, according to their entries in Wikipedia, Actinobacteria, and most Firmicutes are gram-positive and, as these appear to be present in abundance in the human gut of healthy individuals, one assumes that they are not pathogenic to humans.