I have heard it both ways....from mostly rank amateurs actually, so I'll ask people w/ more experience.

Is there a chance that these harbor "nasties" i.e. virus or worse, that can infect whatever unit they are installed in. I am nervous about this, and considering a deal w/ a local gold recovery operation..............

 

Dynamic ram without any power source on the board will reset to default unknown state within a few milliseconds of power removal. Unless someone has intentionally replaced the DRAM with some type of ROM or EERAM there is no chance any code could survive more than a couple of seconds. You should be fine using recovered SIMS.