How to download dbSNP database?
In the dbSNP FTP site you linked, you need to go into organisms and select your organism of interest (human obviously). You can then select which release of the SNP database you want (eg. 150 vs 151) [the modified dates hint at when they were released] and which genome build you want (eg. hg37 vs hg38).

Below I am looking at the .vcf files. I assume this what you want because they can be converted to ADAM format via the adam vcf2adam command.

For example human (newest genome and newest dbSNP release):
ftp://ftp.ncbi.nlm.nih.gov/snp/organisms/human_9606_b151_GRCh38p7/VCF/

Your next decision is whether or not you want to use ALL the annotated SNPs in the database or just the common ones. For the former you choose the All_20180418 file and for the later the common_all_20180418 file. I'm pretty sure the convention here is that the date in the filename is when it was uploaded/updated.

In your case I'm not sure what makes the most sense. Firstly, are you trying to replicate the initial conditions of when that software was published or do you want simply to benchmark the method with the best available data. Besides that, I imagine using all them is computationally much more taxing and if you are just coming up with general trend then using the common ones seems viable.