No that won't work. You can't access tabs with a href in shiny dashboard. You need to use the onclick argument of an a() link and provide a the JS function with the appropriate tab name.
You don't need to know JS to do this, just copy my example above by placing the JS script in the tags$head() ui section and using onclick = "openTab('name-of-tab-to-open')" in any links you want to use as tab selections.
Or if you want the link to open a Modal Dialog, use the actionLink and server logic I used in the first example.
If you want the navbar items to be a dropdown menu you can wrap it in shinydashboards dropdownMenu() function and provide a few additional arguments like so:
dropdownMenu(
headerText = "Tab Menu",
icon = icon("info"),
tags$li(
class = "dropdown",
a("Tab 1",
onclick = "openTab('tab1')",
href = NULL,
style = "cursor: pointer;"
)
),
tags$li(
class = "dropdown",
a("Tab 2",
onclick = "openTab('tab2')",
href = NULL,
style = "cursor: pointer;"
)
)
)
If you need your own customisation of the dropdown have a look at this SO answer.