Yes, my Tacx assembly gel works great on the aluminum stem to bar clamp, and on aluminum seat posts in various frame materials. I've used it on a badly designed saddle clamp with great results (Ritchey WCS seatpost, that depends on friction to clamp onto a curved surface), and on saddle rails. I've still got most of the tube I bought 6 years ago.

I think it's plastic grit in a gel base? If anything, it would help separate the seatpost from the steel, avoiding corrosion. I see Tacx says: " Assembly compound also stops parts distorting or loosening and ensures perfect corrosion protection."