Can you put spacers on top of Specialized adjustable stem? I know that the stem is offset by the angled shims and has an angled top cap, was wondering if there is an angled spacer as well.

I'm curious because I just came across a picture of spacers above a Specialized adjustable stem on ebay - https://cgi.ebay.com/Specialized-Tarm...ht_1921wt_1139

sure you can. IIRC some mtbs come with a spacer on top and their adjustable stem.

When the bolts, åre loose around the fork steerer,
the stem is just another spacer,
as far as the bearing pre-load goes, as adjusted by the top cap bolt.
so its fine in the middle of the spacer stack.