Shielded RJ45 plugs will indeed fit into unshielded RJ45 jacks without a problem.

*MOST* Ethernet equipment (hubs, switches, and network cards) made in the last 6-7 years has shielded RJ45 jacks. Prior to that they had unshielded RJ45 jacks.

However, almost nobody (in the USA) uses shielded cable with that equipment, and it works just as well with unshielded cable.

I believe that the only reason for the prevalence of shielded RJ45 jacks on newer equipment is due to EC (European) regulations requiring them. (Screened twisted pair is a lot more common in Europe than it is in the USA).

Given that Ethernet was designed to run perfectly fine over unshielded/unscreened cable (and if you go back far enough, the 10 megabit variety was designed to run over standard telephone cable--cat 3 cable did NOT exist back then), I believe that screened twisted pair cable is a solution in search of a problem.