Tied notes in Dorico ARE a single musical object, one note that has to be notated with a tie because of metric boundaries. I do not think you can have Dorico write multiple accents on the same note by itself, so you have different options here :
• use the playing technique editor to create accents as a playing technique. It won’t play (at least not without creating some expression map, for which I cannot help you, since I’ve never needed those yet) but you’ll have full freedom about those signs.
• use slurs instead of ties, and tweak them so that they look like ties (if you need).
I realize now that this will probably apply to unpitched percussion instruments. Although these are “a different beast” from the rest of the program, I think my advice stands. There has been a lot of requests about ties and percussions altogether (especially when dealing with tremoli, which by the way has been taken care of in the properties panel).
Hope this helps !