** Can I run 5' of vent under the deck to vent to the outside of the deck? **
* I will probably need a couple of 90's to get me under the joist and then out *
There is a limit to the length and number of elbows a dryer can have installed on it and still allow the dryer to work satisfactorily (see the link below). What those limits are will depend on the brand and model the dryer is.
You should also keep in mind that the dryer vent should be thoroughly cleaned yearly at least and the more elbows there are, the harder that job is going to be.