i use silk threads for applique all the time- i love silk thread- i do not however satin stitch my appliques---never really liked that look - just me-
i do something that's not so (harsh) like a small zigzag or blanket stitch- it works great. silk thread comes in different weights- 60 wt & 100 wt are common- i use 100wt for hand applique and hand piecing- but i think you might want one a bit heavier than that for machine applique- like the 60wt...but try what you have & see how you like it.