Sure why not. Lead Turkey loads tend to be a slower fps due to not shooting at a flying bird. They are just taylored for a tight pattern. Steel shot tends to pattern tighter than lead, higher speed and get blown with a full choke, so you may want to do some pattern testing to determine what choke is best for your load. The only other issue is that the Steel will lose it's downrange energy faster than lead. But again, Turkey is generally a close range affair. Just pattern test to get the best choke combination for a tight pattern for the loads you already have and keep your range under 30 yards, it will kill turkeys IMO.

Here is a Turkey pattern target you can print off to use.

http://mdc.mo.gov/nathis/birds/turkey/images/turk10.gif

with today's modern choke tubes and the new game specific turkey loads from ammunition manufacturers most 3" chambered shot guns with for example a Briley Super Full Turkey choke, can reach out and kill a turkey at 50+ yards! I have in fact killed 3 birds in the last 2 years that hung up on me at 45yds, 49yds & 52yds. I took those shots ONLY because I spent hours at the gun range coming up with the best choke tube/ammo combination I could find for my shotgun......