They did when David Kahn was GM and intent on raiding our roster. Not so sure that's still the case.
Thibs was in the East forever (BOS and CHI). Even in MIN he's 2 time zones away from Portland. The one, and only, time POR and MIN met in the playoffs was 19 seasons ago. Doesn't sound like much of a rivalry to me.
Being in the same division does not increase the likelihood of meeting in the post season, and winning the division got bumped down to second tie breaker (after head to head record) in 2016. Sure trading him to the East means only seeing him twice a year and further decreases the likelihood of meeting him in the playoffs (assuming the NBA doesn't adopt a 16 best teams playoff regardless of conference format), but sending him to POR is no worse than sending him to any other team in the West, and actually better than having him end up someplace like GSW, HOU, SAS, LAL, etc.
BNM