There are at least four of them.
Betsy Randle- recurred as Jill's best friend Karen on Home Improvement before she left to play Amy Matthews full time on Boy Meets World
Blake Clark- recurred as Harry the hardware store owner on Home Improvement and recurred as Shawn's father Chet Hunter on Boy Meets World
Richard Karn- played Al Borland full time on Home Improvement and guest starred as an animal control officer on Boy Meets World
Mickey Jones- recurred as Pete Bilker on Home Improvement and guest starred as an employee at Alan's store on Boy Meets World

Here's a list of 58 people who imdb.com connects to both shows in some capacity:

https://www.imdb.com/search/name/?roles=tt0105958,tt0101120

This page lets you search for people common to any two shows:

https://www.imdb.com/search/common/?ref_=adv_srch_title_tab

Here's a list of 58 people who imdb.com connects to both shows in some capacity:

https://www.imdb.com/search/name/?roles=tt0105958,tt0101120

This page lets you search for people common to any two shows:

https://www.imdb.com/search/common/?ref_=adv_srch_title_tab