Difference between Welsh rabbit and beer cheese dip
The similarities…
Fat, flour, cheese, milk
The differences…
Welsh Rarebit - English mustard, Worcestershire sauce
Beer cheese dip - garlic, paprika, dijon mustard, beer [optional in rarebit]
You might swap one for the other, but warn your diners first which they're getting.
If I got garlic in Welsh rarebit I'd probably not eat it, wondering what the heck was wrong with it. if I knew it was meant to be there beforehand, I probably would.
Similar could be said for the Dijon [too vinegary] &amp; paprika [odd colour even before tasting].
I'd eat either &amp; probably enjoy it, so long as I knew what I was getting before I tasted it; otherwise you get that odd mental trip-up like when you think you've been served tea but it's actually coffee. It's revolting until you realise, then it's fine.
BTW, rarebit works really well for Philly cheesesteak ;)