can i use a dell monitor with a mac mini?

Mine works great! And hear reports of many other happy users.

Dell has traditionally been the way to get a nice monitor at less than Apple prices. Plus they have a 3-year warranty.

And they periodically go on sale.

Having said all that, which model do you have in mind?

There is no reason you couldn't do this. You can plug a monitor to the mini either via vga (adaptator provided)or dv-i connection so this should be OK for most monitors.
you just have to check what resolutions your monitor can display and compare it to the resolutions that the mini can generate to decide which one would be the best compromise.

The Dell display will undoubtedly connect to the mini, and work with it, regardless of which model. However, while most of their models will work well with a Mac mini, there have been some which render rather less than ideal results - slightly greyish or fuzzy images.

If the display is a CRT model or an LCD panel which connects via either VGA (analog) or DVI (digital) then it should work perfectly. If, however, it's an LCD with analog-only (VGA) connector, and it is a 15 or 17" model from approximately 2 years ago, you may find slightly dim or blurry output. Still usable and mostly correctable with adjustments to display and MacOS preferences, but not as perfect as other screens.