In the face of the new Lockheed Martin F-35s coming into service, Boeing have also been selling more EA-18G Growlers to the Pentagon.
The article linked above debate the pros and cons of purchasing more Growlers (the Navy has already been purchasing more and Congress is granting them more Growlers, regardless of anyone else's opinion, and the Marines and Air Force are more keen on the brand new F-35):
Stealth will degrade over time. Not because of difficulty of maintenance, but because enemy Area Denial technology will continuously improve. And it would be best to approach Anti-Access/Area Denial threats tactically.
"Stealth is 'delayed detection' and that delay is getting shorter. SAM (Surface-to-Air Missile) radars are shifting their frequencies into lower frequency bands where U.S. stealth is less effective; Early warning radars are in the VHF spectrum where stealth has limited if any capability. These radars are networked into the SAM radars giving the SAM radars cued search. The threat is developing out of spectrum sensors like IRST [infrared search and track] systems on their fighters. Stealth has no capability to delay an IRST detection and track."
-Mark Gammon, Boeing's F/A-18E/F and EA-18G program manager for advanced capabilities
With that being said, F-35s are not absolutely stealthy, they are still visible with low frequency ATC radar due to frequency resonance. While the larger B-2 Spirit is less vulnerable to such signals.
Aside from the LO features, the F-35s have limited (a single X-band) radar jamming capabilities in the front, and nothing rearward for disengagements.
It may be an industry rivalry between Boeing and LM, but both machines will have to play well together on the battlefield rather than fight each other. There has been criticisms for the lack of compatibility of the Growler. With the F-22 using a proprietary Intra-Flight Data-Link to talk to other Raptors, while the F-35 uses a Joint Strike Fighter-only Multifunction Advanced Data-Link.
Boeing's Gammon has commented that "Growlers have Link 16 which is compatible with [the] F/A-18 Super Hornet and F-35, E-2D, F-15, F-16, and most of the bombers". The F-35 can be fitted with a Link 16 data system but will not be using the data link in a SEAD mission since it will give away their own position.
Also realize, as I have learned from this article, the Growler are not to be placed in the same role as a traditional Wild Weasel strike aircraft. It still operate in a key role in SEAD/DEAD missions to clear out enemy air defenses, however. Growlers provides forward (when entering) and rearward cloaking (when leaving) via signal jamming. Growlers also quarterback the mission by relaying key enemy assets for air superiority/strike fighters or bombers to target destroy ATC radar, higher frequency targeting radar, and SAM launch platforms.
Think of EA-18G Growlers as a Protoss Arbiter from Starcraft; You would fly ahead to jam signals (produce a LOT of noise), essentially rendering you a red hot target and the F-35s behind you entirely invisible.
(Here's an Arbiter providing cover for some Reavers)